Indication for liver biopsy (modified from Ref. ).
Liver fibrosis, that is, excessive accumulation of extracellular matrix protein, occurs and is the wound‐healing response and common final pathway of various chronic liver diseases. Advanced hepatic fibrosis caused by chronic liver inflammation eventually progresses to cirrhosis, and prognosis and management of chronic liver diseases depend on the fibrotic severities. Therefore, the early and precise evaluation of severity and status of liver fibrosis provides useful information for diagnosis as well as treatment planning and treatment efficacy and prognosis. Although invasive liver biopsy is the gold standard to assess the nature and severity of hepatic fibrosis, it has several recognized limitations including sampling error and inter‐observer variability in interpretation and staging. Furthermore, the dynamic process of fibrosis resulting from progression and regression is difficult to capture with biopsy alone. Therefore, alternative, simple, reliable, and noninvasive direct and indirect serum markers able to predict the presence of significant fibrosis or cirrhosis in patients with chronic liver disease with considerable accuracy were needed. The hepatology experts are actively researching noninvasive methods of fibrosis quantification. The aims of this chapter were to review the nature and limitations of the several noninvasive methods for the assessment of presence and severity of liver fibrosis in patients with chronic liver disease.
- noninvasive method
- stage of liver fibrosis
- chronic liver disease
Liver fibrosis and cirrhosis are an important and growing global health problem. Patients with non‐cirrhotic chronic liver disease may have an increased mortality rate compared to controls . However, mortality and morbidity rates increase exponentially once cirrhosis develops. Prognosis and management of chronic liver diseases greatly depend on the amount and progression of liver fibrosis. Therefore, the ability to reliably rule out cirrhosis may be considered an important characteristic of any test designed to assess liver fibrosis . The diagnosis of cirrhosis also portends an increased risk of liver‐related morbidity  as well as mortality . Liver‐related mortality and decompensation are expected to continue to increase over the next decade, due to the projected increase in the number of patients with advanced liver fibrosis in the population . Therefore, the accurate and timely evaluation of liver fibrosis is a key step to manage a chronic liver disease and to assess its prognosis and in need of close monitoring, management of complications, and underlying liver disease in patients with advanced stages . For many years, liver biopsy has been considered the “gold standard” for evaluation of liver fibrosis . Pathologists have proposed robust scoring system for staging liver fibrosis such as the semi‐quantitative Metavir score (F0: no fibrosis, F1: portal fibrosis, F2: bridging fibrosis, F3; bridging fibrosis, and marked, F4: cirrhosis)  and the modified Ishak score, an expansion of Metavir score . In addition, computer‐aided morphometric measurement of collagen‐proportional area, a partly automated technique, provides an accurate and linear evaluation of the amount of fibrosis . However, liver biopsy is an invasive procedure with rare but potentially life‐threatening complications and prone to sampling errors. Also, liver biopsy gives a snapshot and not an insight into the dynamic changes during the process of fibrogenesis (progression, atatic, or regression). Therefore, liver biopsy has some limitations as follows. First, biopsy is an invasive technique, which has associated morbidity; pain occurs in 20% of patients and major complications such as bleeding or hemobilia in 0.5% . The bleeding rate (0.5%) has not changed significantly in recent years, according to a large multicenter study . The primary factor that appeared to contribute to bleeding risk was platelet count rather than qualitative factors such as operator experience, needle size, or the use of ultrasound to localize the site. Second, the small size of the biopsy makes it prone to sampling variability . Third, the interpretation of the histologic changes can be problematic with inter‐ and intra‐observer variation . These limitations as well as the availability of powerful viral diagnostic tools and new antiviral drugs have rapidly decreased the use of liver biopsy in viral hepatitis and led to the development of noninvasive techniques for the assessment of liver fibrosis. On the other hand, at least some correlation between biopsy stage and outcomes has begun to emerge. In the NIH‐HALT C cohort, a correlation was found between the Ishak fibrosis stage and clinical outcomes, the need of liver transplantation, and liver‐related deaths in patients with chronic HCV. However, even in this study, up to 25% of the liver biopsy samples were fragmented, which significantly diminished the ability to draw correlations between biopsy findings and clinical outcomes . While some of these methodologies are now generally applied in patients for a top priority of evaluation, biopsy exists within the clinical technique of hepatologists for estimating the causes of complicated diseases or when there are unconformities between clinical characteristics and extents of fibrosis evaluated by noninvasive methodologies . The dynamic process of fibrosis should be best measured as a continuous variable and classical histological staging systems do not permit this . Since liver biopsy is an invasive procedure, cost‐intensive, mostly uncomfortable for the patients, and sometimes prone to complication, alternative, simple noninvasive tests have been developed to reliably assess the stage of liver fibrosis. Ongoing efforts include serum markers and imaging based on ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI). The goal is to develop tests with high specificity and sensitivity to estimate liver fibrosis and predict outcomes . Ideally, noninvasive methodologies of liver fibrosis should be liver specific, easy to perform, reliable, and inexpensive. In addition, it should be accurate not only for the staging of fibrosis but also for the monitoring of disease progression and antiviral therapy efficacy . Scientific attention is currently focused on new antifibrotic therapies, aiming at fibrosis reversibility and cirrhosis regression . It is therefore important, now more than ever, to ensure accurate and prompt assessment of hepatic fibrosis in therapeutic trials of chronic liver disease. Consequently, the demand for noninvasive method substitutes to estimate hepatic fibrosis is a main trial that has provoked research and induced the improvement of noninvasive serological markers of hepatic fibrosis. Several noninvasive serological markers have been described to forecast the existence of significant fibrosis or cirrhosis in patients with chronic hepatic disease with good accuracy. However, most of these markers require complicated calculations, and manipulation in various clinical situations is difficult and inconvenient . Recently, transient elastography (TE, FibroScan) has been introduced as a novel, rapid, noninvasive, and reproducible method to measure liver stiffness . In several studies [22, 23], liver stiffness measurement (LSM) using M probe of FibroScan accurately predicted hepatic fibrosis and cirrhosis in patients with chronic liver disease.
This chapter focuses and provides comparison of invasive and noninvasive methods for assessing the severity of liver fibrosis and aims to provide update on noninvasive diagnostic and prognostic assessment tools for liver fibrosis and cirrhosis in patients with chronic liver disease.
2. Mechanism of liver fibrosis
Liver fibrosis is the result of the continuous wound‐healing process of the liver to repeated damage . After acute liver injury (e.g., viral hepatitis), parenchymal cells regenerate and replace the necrotic or apoptotic cells. The process is associated with a hepatic inflammatory response and a limited deposition of extracellular matrix (ECM) in the hepatic parenchyma. If the liver injury persists, then eventually the liver regeneration fails, and hepatocytes are substituted with abundant ECM, including fibrillar collagen . This process results in cirrhosis, which can have a bad outcome and high mortality. Progression to this end stage is typically variable but slow, developing over 20–40 years in patients with chronic liver damage; the speed is dependent on both genetic and environmental factors . Liver fibrosis is a common pathological consequence of a variety of chronic stimuli, including viral, alcohol, and autoimmune, drug‐induced, cholestatic and metabolic diseases [18, 26–28]. Deposition of excess ECM is rich in fibril‐forming collagens , which change the normal structure of the liver resulting in pathophysiologic damage to the organ . Liver fibrosis is beneficial at first because it can encapsulate the injury and is considered a reversible process at this stage . In normal liver, ECM is highly dynamic substratum with a precisely regulated balance between synthesis and degradation. Normally, the hepatic ECM comprises less than 3% of the relative area on a liver tissue section and approximately 0.5% of the total wet weight of liver . It is also a component of Glisson’s capsule, portal tracts, central veins, and the subendothelial space of Disse. The most important structural ECM components in liver are collagen, proteoglycans, laminin, fibronectin, and matricellular proteins. The hepatic parenchyma is composed of hepatocytes, endothelial cells, and other resident cells, including hepatic stellate cell (HSCs) and Kupffer cells (KCs). The sinusoid is the hepatic microvascular unit that has an endothelial lining distinguished by fenestration of pores and is separated from the hepatocytes by the space of Disse, where HSCs reside. This space contains a low‐density basal membrane‐like matrix that is essential for maintaining the differentiated function of parenchymal cell yet is sufficiently porous to enable metabolic exchange between the bloodstream and hepatocytes . During chronic liver injury, however, ECM production exceeds ECM degradation, and liver fibrosis develops as results of the progressive thickening of fibrotic septae and chemical cross‐linking of collagen. Moreover, these changes in ECM composition directly stimulate fibrogenesis (Figure 1) . After liver injury, disruption of this matrix and replacement by fibrillar collagens I and III and fibronectin have occurred [34, 35]. Fibrosis is characterized histologically and biochemically by a several‐fold elevation in the total ECM content of the liver .
Accumulation of ECM in the space of Disse leads to loss of the normal fenestrating structures that are characteristic of the endothelial lining, which causes the impairment of the normal bidirectional metabolic exchange between portal blood and hepatocytes. This process is sinusoidal remodeling, termed capillarization of the sinusoid . All major constituents of normal ECM are represented, to some extent, in the newly formed matrix during the fibrogenic process. As in normal ECM, collagen (especially types I and III) and elastin are most abundant proteins, but glycoproteins (fibronectin and laminin) and pure carbohydrates are also present. When compared to normal matrix, scar tissue produced in liver fibrosis has a significantly higher percentage of type I collagen . ECM deposition occurs as a result of an imbalance between excessive ECM production and less degradation. In the normal liver, matrix metalloproteinases (MMPs) have a well‐described ECM‐degrading function. The activity of MMPs, however, is suppressed in the setting of liver injury as a result of overexpression of tissue inhibitor of metalloproteinase (TIMPs) by the activated HSCs . TIMPs are key regulators of MMPs, by blocking their collagenolytic activity. In addition, TIMP‐1 is anti‐apoptotic toward HSCs, in part through the induction of Bcl‐2, thus promoting the survival of fibrogenic cells . This balance between MMPs and TIMPs is crucial for ECM homeostasis . In human liver, the degree of TIPM‐1 expression correlates with the extent of liver fibrosis . In order to preserve matrix homeostasis, ECM also contains MMPs, MMP‐1, MMP‐8, and MMP‐13 that degrade the fibrillary collagen types I and III predominating in fibrosis, while MMP‐2 and MMP‐9 degrade collagen types IV as well as denatured fibrillary collagens. HSCs are the key source of both MMPs in liver. Although the increase of MMP production should control the excessive increase of the ECM, it can also promote injury. Early increases in MMP, particularly MMP‐2, degrade normal matrix and recruit cells that amplify fibrosis [43, 44]. In addition, there is also enhanced secretion of TIMP‐1 and ‐2 by HSCs during progressive tissue injury and cellular activation. Different populations of cells play roles in fibrogenesis, but the activation of HSCs is an essential factor in fibrinogenesis . The mechanism of liver fibrosis is thought to be associated with the hepatic damage of various etiologic factors followed by the activation of HSCs within the liver that develop into liver myofibroblasts (LMFs) . LMFs include a heterogeneous population of highly proliferative cells that accumulate at injury sites and promote ECM accumulation . The pool of LMF originates mainly from liver mesenchymal cells, namely HSCs . Although HSCs are the primary source of LMFs in liver fibrosis, extrahepatic precursors such as bone marrow‐derived mesenchymal cells and portal fibroblasts contribute in ECM production [49, 50]. HSCs are resident peri‐sinusoidal cells in the subendothelial space of Disse between hepatocytes and sinusoidal endothelial cells. The main cells affected by liver fibrosis are the HSCs and fibroblasts, which are activated by soluble mediators produced by activated KCs or inflammatory cells in the course of chronic liver disease . ECM may thereby regulate cellular activity and availability of growth factors. For instance, decorin and biglycan, two ECM components, bind transforming growth factor‐β (TGF‐β), fibronectin and laminin bind tumor necrosis factor‐α (TNF‐α), and collagen binds platelet‐derived growth factor (PDGF), hepatocyte growth factor (HGF), and interleukin‐2 (IL‐2). The binding of survival factors to the ECM may prevent apoptosis of hepatocyte in the pathologic condition and also prevent growth factor degradation . In liver tissues, HSCs store retinoids such as vitamin A and produce glial fibrillary acidic protein (GFAP), the so‐called fat‐storing cells or vitamin A‐rich cells . Following liver injury, HSCs become activated, which leads to the conversion of a quiescent to activated HSCs that has lost vitamin A droplets, leading to increased proliferation and contraction and the release of proinflammatory, profibrogenic, and promitogenic cytokines. These activated HSCs are capable of enhanced migration and deposition of ECM components [46, 53]. The activation of HSCs can be divided into two stages: initiation and perpetuation . In the first or initiation phase, HSCs undergo the initial changes toward a myofibroblast‐like cell differentiation and become more responsive to proliferative and fibrogenic cytokines by up‐regulation of membrane receptors . This stage also called a “pre‐inflammatory” stage refers to early changes in gene expression that result primarily from paracrine stimuli derived from damaged resident liver cells (sinusoidal endothelial cells, KCs, and hepatocytes) and platelets. KCs engagement drives release cytokines (especially TGF‐β) and ROS signaling . Endothelial cells participate in the conversion of latent TGF‐β into active form and produce fibronectin, which also provokes early HSC activation. In addition, PDGF, TGF‐β, and endothelial growth factor (EGF) which is potent activators of HSCs . Persistence of these stimuli accompanying sustained injury leads to a perpetuation stage regulated by autocrine and paracrine stimuli. Perpetuation stage involves at least seven distinct changes in HSC behavior, including proliferation, chemotaxis, fibrogenesis, contractility, altered matrix degradation, retinoid loss, and inflammatory signaling . Therefore, a critical event in liver fibrogenesis is that the ECM is a dynamic structure, and even advanced fibrosis may be reversible [58, 59]. Multiple interactions between the ECM, HSCs, endothelial cells, and immune cells have been identified. The central event in liver fibrogenesis appears to be the activation of HSCs, which is a complex process . Different patterns of fibrosis progression have been described on the basis of their etiology, region of injury (e.g., portal or central), the source of fibrogenic cells involved, and the predominant fibrogenic mechanisms . For example, chronic viral hepatitis B and C are major causes of bridging fibrosis, resulting in the formation of portal‐central fibrotic septa. Perisinusoidal or pericellular fibrosis is typically found in alcohol‐related disorders and nonalcoholic fatty liver disease (NAFLD). Progression of hepatic pathology with sustained fibrogenesis leads to cirrhosis, which is not merely the end‐stage accumulation of scar, but rather is characterized by a destruction of the hepatic parenchyma and vascular architecture. The main pathological characteristic of cirrhosis is the formation of nodules of regenerative parenchyma enclosed by fibrotic septa, which may contain terminal hepatic venules and portal tracts when the nodules are especially large (i.e., macronodular cirrhosis). Portosystemic shunts and venous occlusion often occur, leading to impairment in liver function and the development of portal hypertension. The formation of vascularized fibrous septa that link portal tracts and central veins is stimulated by angiogenesis and contributes to portosystemic shunting that bypasses the liver parenchyma .
3. Liver biopsy: pros and cons, and limitations
Liver biopsy is usually known as the most specific test to evaluate the feature and severity of liver pathology and can be useful in monitoring the efficacy of various treatments. There are currently several techniques available for obtaining liver tissue and each of these has pros and cons . The size of the biopsy specimen, which varies between 10 and 30 mm in length and between 1.2 and 2 mm in diameter, represents only 1:50,000 of the total mass of liver . Therefore, in disease affecting the liver in a diverse way, the histologic findings of biopsy specimen may not be representative of the pathologic process. However, most cases of chronic liver disease causing fibrosis, such as viral and autoimmune hepatitis, as well as nonalcoholic steatohepatitis (NASH), affect the liver in a relatively uniform pattern . Then the extent, to which the biopsy will be representative, will depend greatly on the size of the specimen obtained. The number of portal triads present in the specimen is important; most hepatopathologists are satisfied with a biopsy specimen containing at least 6–8 portal triads. The indications of liver biopsy are outlined in Table 1 .
|◈ Diagnosis, grading, and staging of chronic hepatitis C or chronic hepatitis B.|
|◈ Diagnosis, grading, and staging of alcoholic liver disease, nonalcoholic steatohepatitis (NASH), or autoimmune hepatitis|
|◈ Diagnosis of heavy metal storage disorders (e.g., hemochromatosis, Wilson’s disease)|
|◈ Evaluation of the cholestatic liver disease, primary biliary cirrhosis, and primary sclerosing cholangitis|
|◈ Evaluation of abnormal results of biochemical tests of the liver in association with serological workup that is negative or inconclusive|
|◈ Use of hepatotoxic regimens (e.g., methotrexate therapy for psoriasis): monitoring|
|◈ Diagnosis of liver mass (e.g., cancer or unexplained lesions)|
|◈ Liver donor status before transplantation|
|◈ Evaluation of systemic illness (e.g., fever of unknown origin, inflammatory or granulomatous disorders)|
|◈ Hepatosplenomegaly of unknown cause: diagnosis|
Even for patients where serological tests point to a specific liver disease, a liver biopsy can provide valuable information regarding staging, prognosis, and management. There are bad interrelationships between clinical characteristics or status of serum liver enzymes and hepatic histopathologic findings, but also patients with healthy status of liver enzymes may be diagnosed to have clinically advanced fibrosis or cirrhosis on histopathologic findings . If the patient has minor‐state illness and is infected with genotype 1a or 1b of the hepatitis C virus, a medical judgment may be made to delay treatment. If the patients have the above degree of moderate disease, treatment will be commonly suggested. If the patients have a virological reaction and acceptable adverse reactions with treatment, continued therapy would be firmly encouraged. The cirrhotic findings on hepatic histopathology will indicate the need for extra tests, such as upper endoscopic procedure to rule out esophageal varices and monitoring for hepatoma with continuing assessment of serum α‐fetoprotein and hepatic sonography . In alcoholic liver disease (ALD), the grade of the clinical symptoms and the severity of serum liver enzymes elevation correlate poorly with the degree of liver pathology, particularly in patients who continue to consume alcohol. The long‐term prognosis depends upon the extent of liver damage . In patients with ALD as well as NASH, liver biopsy may demonstrate hepatic fatty infiltration, ballooning degeneration of hepatocyte, Mallory’s bodies, and hepatonecrosis, regardless of clinically severe fibrosis or cirrhosis . In primary biliary cirrhosis (PBC), sequential liver biopsies may assist one to investigate the natural history, track the responses of therapy, or identify a recurrence of the disease after liver transplantation [66, 67]. Liver biopsy allows a precise evaluation in approximately 90% of patients with obscure disorders revealed on liver function tests . The explanation of diverse courses that appear in a transplanted liver including immune reaction, systemic or infectious complications, drug toxic reaction, and the recurrence of primary disease necessitates a liver histological examination . Liver biopsy can also provide the diagnosis of systemic diseases that can influence the liver, such as sarcoidosis, lymphoma, acquired immune deficiency syndrome (AIDS), and amyloidosis. The histopathological examination of the biopsy material is a subjective process; therefore, diagnostic reproducibility at the 100% level is practically impossible. Intra‐observer and inter‐observer agreement studies suggest that biopsy specimen size and observer experience (specialization, duration of practice, and academic practice) are important factors in reducing the variation of assessment [8, 70]. Most studies of specimen adequacy have focused on chronic hepatitis because it represents the most common indication for liver biopsy . At present, the most common suggestions for the precise assessment of the degree of fibrosis in chronic hepatic diseases are that the size of biopsy tissue materials must be at a minimum of 20 mm in size and 1.4 mm in radius and must be retained at a minimum of 11 intact portal tracts . In addition, the type of biopsy needle is important, as suction needles tend to miss the fibrous tissue of the septa, as opposed to cutting needles, thus providing the wrong impression regarding the degree of fibrosis and the presence or absence of cirrhosis . Finally, it should be kept in mind that biopsy specimens obtained from subcapsular locations generally contain more fibrous tissue than deeper specimens taken perpendicular to the hepatic surface. For many years, liver biopsy has been considered the gold standard for the staging liver fibrosis . For instance, in patients with chronic HCV, precise definition of the liver fibrosis stage is the important parameter to assess the risk of disease progression and to decide the need for immediate antiviral therapy . Several standardized semi‐quantitative scoring systems have been proposed for the staging histological activity index (HAI) proposed in 1981 by Knodell  and, more recently, the Ishak score  and the Metavir system  (Table 2). All of these scoring systems have some limitations, being not linear and prone to intra‐ and inter‐observer variation and to sampling variability .
|Fibrosis of some portal areas without septa||1||1||1||1||1||1|
|Fibrosis of most portal areas without septa||1||2||1||1||1||2|
|Portal fibrosis with few septa||3||3||2||2||2||3|
|Septal fibrosis without cirrhosis||3||4||3||2||2||3|
The Knodell score is a composite score that is based on histological assessment of periportal and/or bridging necrosis, intralobular degeneration and focal necrosis, portal inflammation, and fibrosis. The score ranges from 0 to 22, with higher scores representing more advanced disease . Knodell score is frequently used in trials of treatments for chronic hepatitis, particularly HCV. The score is used to assure that baseline histologic features in treatment groups are equally matched and to assess histologic changes after therapy. A limitation of the Knodell score is that it combines inflammation and fibrosis to arrive at one composite score, so it is relatively insensitive to changes in fibrosis. This is important because it is fibrosis, and not inflammation per se, that leads to many of the sequelae of chronic liver disease. In addition, patients may have the same Knodell score despite having markedly different degree of fibrosis. Also, the Knodell score is associated with high inter‐ and intra‐observer variability. The Metavir system is a semi‐quantitative classification that consists of four intensity degrees of an activity score (A0–A3) and a five‐point scale of fibrosis (F0–F4) [8, 76]. In contrast to the Knodell score, the Metavir system was specifically designed and validated for patients with HCV . The inter‐ and intra‐observer reliabilities of the activity and fibrosis scores of the Metavir system are similar to the Knodell score. The Ishak score is a modification of the Knodell score that includes six stages of fibrosis . This permits documentation of small changes in fibrosis compared with the standard Knodell score, which has only four stages. This staging system has become widely used in clinical trials because of its ability to detect mild changes in fibrosis . The Scheuer system is a simple scoring system that separates necrotic inflammation from fibrosis . Histologic findings of portal inflammation, interface hepatitis, and lobular inflammation are each assigned a score of 0–4. A separate score (0–4) is assigned to the stage of fibrosis. Batts‐Ludwig system is also known as the modified Scheuer system . This system is applicable to both chronic viral hepatitis and autoimmune hepatitis and is more useful for assessing an individual patient’s liver biopsy for clinical care than therapeutic trials. In addition, disease‐specific scoring systems are also available, including scoring systems for nonalcoholic fatty liver disease (NAFLD), ALD, primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). However, it is not common to encounter two or more concurrent diseases in a liver biopsy specimen, no scoring systems are available that specifically address these situations . Absolute contraindication to liver biopsy includes patient’s inability to remain still and to maintain brief expiration for the procedure, suspected vascular lesion (e.g., hemangioma), bleeding tendency (e.g., INR >1.2 despite receiving vitamin K, bleeding time >10 min), and severe thrombocytopenia (<50,000/mL). Relative contraindications include profound anemia, peritonitis, marked ascites, high‐grade biliary obstruction, and a subphrenic or right pleural infection or effusion. Nonetheless, percutaneous liver biopsy is sufficiently safe to be performed on an outpatient setting . Despite liver biopsy being the standard test for an appropriate assessment of patients with chronic liver diseases, there are several limitations of this including variable quality of liver biopsy specimens of <20 mm in length which may be difficult to interpret. Therefore, larger caliber needles may yield better than fine‐needle biopsies . Because of fluctuating disease activity, histologic changes obtained at a single point in time may not reflect overall disease activity, which may vary. On the other hand, one would often want to be aware of the progression of liver disease in order to assess therapy response. Limitations entailed by repeat liver biopsy as regards potential patient’s risks demand the development of new methods for liver fibrosis evaluation. The features and limitations of liver biopsy are summarized in Table 3. On all these grounds, noninvasive diagnostic tests (serum markers and imaging modalities) have been developed of late mainly to assess liver fibrosis severity. The following pages attempt to describe available information on the better‐known serum markers as well as imaging techniques.
|Liver biopsy||Noninvasive methods|
4. Noninvasive assessment of liver fibrosis in patients with chronic liver disease
Liver biopsy remains the “gold standard” of assessing hepatic fibrosis. However, it has limitations, such as high cost, invasiveness, associated risk for complications, and sampling or observer variability. Therefore, liver biopsy has recently been challenged by the development of novel noninvasive modalities, including serum direct and/or indirect markers of hepatic fibrosis, noninvasive modalities of predicting fibrosis and imaging techniques, including TE (FibroScan), ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI), and thallium 201 per rectal scintigraphy (TI‐201 test). As well as TE [85, 86], TI‐201 test is a relatively new technique for assessment of liver fibrosis or cirrhosis [87–91]. However, the cost of the equipment may limit the use of TE in some institutions with limited resources. In the past decade, several noninvasive methods for assessing hepatic fibrosis have been published, resulting in more noninvasive tests than histologic scoring systems. The noninvasive tests were introduced to estimate the likelihood of advanced liver fibrosis in patients with chronic viral liver disease at presentation, and on follow‐up to assess fibrosis regression in post‐treatment period . These tests were later applied in ALD [93, 94] and NAFLD [95, 96]. Our previous studies on the clinical value of the TI‐201 test in chronic liver disease may be useful in differentiating chronic hepatitis from cirrhosis and prediction of its prognosis for the management of disease [90, 91, 97, 98]. The first important clinical topic in the assessment of new diagnostic methodologies for evaluation of liver fibrosis is its validation against the present clinical gold standard, liver biopsy, to calculate sensitivity, specificity, and negative‐ (NPV) and positive‐predictive values (PPV). The standard statement of the efficiency of modalities is to examine the area under the receiver operator characteristic curve (AUROC), which plots the sensitivity over 1‐specificity using liver biopsy as the reference . The AUROC indicates the probability that a test will correctly rank two randomized patient groups, one with a liver biopsy considered “normal group” and the other “diseased group” [99, 100]. Because liver biopsy itself is not a perfect gold standard, a perfect test will never reach maximal value (1.0) . According to a range of accuracies of the biopsy and a range of prevalence of significant disease (that influence the AUROC), an AUROC of >0.90 in the most favorable scenario cannot be achieved when assessing the so‐called “significant fibrosis” even for a perfect marker [99, 101]. This is important for several reasons. First, studies have already shown that these maximal AUROC values have been reached for surrogate markers, especially when assessing cirrhosis versus non‐cirrhosis, suggesting that these surrogate markers may be at least as good as liver biopsy in the diagnosis of cirrhosis . Second, some reports suggest that a definitive method for assessing the performance of surrogate markers would employ a clinical end point rather than biopsy as gold standard . The AUROC values may also depend on the biopsy tissue size and fragmentation  as well as the incidence of each stage of fibrosis within the studied population (e.g., the spectrum bias) . Indeed, if extreme stages of fibrosis (F0 and F4) are overestimated in a population, the sensitivity and specificity achieved will automatically be higher than in a population that included only patients with near stages of fibrosis (F1 and F2). Several strategies of prohibiting the “spectrum bias” have been suggested including the realignment of AUROC by the DANA method that define advanced (F2–F4) and non‐advanced fibrosis (F0–F1)  or the Obuchowski measure that is multinomial version of the AUROC [105, 106]. Today, noninvasive methods are widely available. Their most advantages are the absence of contraindication and dangerous complications for the patients, and their reproducibility . In contrast to liver biopsy, many noninvasive methods can effectively evaluate the extent of fibrosis in the whole organ and not only in a part of it. Their potential ability to identify and differentiate between advanced fibrosis stages, the high specificity and sensitivity to diagnose cirrhosis, and their easy application makes them a useful tool in daily clinical practice. Many liver fibrosis experts would therefore consider noninvasive fibrosis tests with an AUROC of 0.85–0.90 to be as good as liver biopsy for diagnosis and staging for liver fibrosis . The role of noninvasive diagnostic tests becomes more significant because their diagnostic accuracy can be increased if they are combined, that is, a serological panel may be used in conjunction with an imaging technique [90, 99, 109]. Features of ideal noninvasive markers of liver fibrosis are summarized in Table 4.
|◈ Liver specific|
|◈ Levels not influenced by alterations in liver, renal, or reticuloendothelial function|
|◈ Measurement of one or more of the following processes: Stage of fibrosis, imbalance of activity of ECM (fibrogenesis vs. degradation)|
|◈ Easy to perform|
4.1. Serological markers of liver fibrosis
The clinical need for good noninvasive markers of fibrosis is underlined by the marked increase in the number of reports in this area in recent years. A large number of the serological markers of liver fibrosis have been assessed for the noninvasive evaluation of liver fibrosis and are broadly categorized into two groups (direct and indirect) . First, we will refer to direct markers of fibrosis that are thought to directly reflect ECM turnover. Fields in which these methods may have clinical or investigational values involve both the noninvasive method for staging of liver fibrosis but they may also be useful for monitoring the behavior of fibrogenesis and ECM metabolism. Therefore, such assays may be valuable in forecasting fibrotic disease deterioration as well as the efficiency of treatment. Second, there are those that reflect changes in hepatic function but do not directly reflect ECM turnover, for instance, platelet count, coagulation studies, and evaluation of liver enzymes, the so‐called indirect markers of liver fibrosis. Researches and developments of these markers have largely focused on the diagnosis of cirrhosis, but more recent researches have emphasized the availability of these markers to assess patients with more advanced fibrosis and hence may be valuable in guiding treatment decisions and prediction of complications of liver cirrhosis [90, 108].
4.1.1. Direct markers of liver fibrosis
Direct markers of liver fibrosis include serum markers, which have been shown to be, or are thought to be, directly involved in the deposition or degradation of ECM. The best‐validated marker is hyaluronic acid (HA), a glycosaminoglycan synthesized by HSCs . HA levels correlate with fibrosis in ALD  and chronic viral hepatitis [112, 113] and a highly negative score may be used in clinical practice as a reliable index for exclusion of liver fibrosis. Amino‐terminal propeptide of type III collagen is a marker associated with collagen deposition and its level is increased in acute and chronic hepatic diseases . TIMPs (TIMP‐1 and ‐2), on the other hand, are associated with the procedure of collagen degradation, which is progressive to fibrosis consequence . The direct markers include several cytokines and markers of matrix turnover (Table 5). The circulating retention times of these molecules are short, so levels may reflect the behavior of ECM turnover. Since ECM turnover is related to both new ECM accumulation and degradation and rebuilding of formed ECM, circulating levels probably exhibit both the activity of the fibrogenesis and the total amount of ECM rebuilding . This phenomenon is identified by at least three properties. First, circulating amounts of these markers are often most increased in situations with rapidly processing fibrosis (e.g., advanced ALD or more active viral hepatitis) and may be high ahead of the significant accumulation of ECM [113, 115]. Second, circulating ECM levels tend toward a decrease in reaction to therapy of the underlying illness, often before any perceptible decrease in the stage of fibrosis . Third, in chronic liver diseases, elevations of several, but not all of these markers associate independently with the stage of fibrosis, rather than with either serological or histopathological findings of inflammatory reaction [112, 117, 118]. In some studies, however, levels of these markers correlated more strongly with the degree of histopathological inflammation or serum liver enzymes . The observation that markers of ECM metabolism are increased in parallel with markers of liver inflammation and necrosis may reflect the importance of these processes in up‐regulating fibrogenesis. Direct markers of fibrosis can also be categorized according to their molecular structures. These include (a) collagens: procollagen I and III, propeptides released into the circulation during matrix accumulation and rebuilding. Type IV collagen, which is secreted during interstitial filament metabolism, reflects matrix depletion and rebuilding; (b) glycoproteins and polysaccharides including HA , laminin , tenascin, and YKL‐40 ; and (c) collagenase and their inhibitors, include the MMPs and TIMPs, and cytokines involved in liver fibrosis, the best studies of these is TGF‐β. Others, including PDGFs and the antifibrotic cytokine IL‐10, have been less well evaluated . The greatest clinical utility of HA may be its ability to exclude patients with significant fibrosis and cirrhosis .
|Markers of deposition||Markers of degradation||Unknown roles|
|◈ Procollagen I C‐terminal||◈ Procollagen IV C peptide||◈ Hyaluronic acid(HA)|
|◈ Procollagen III N‐terminal||◈ Procollagen IV N peptide (7‐S collagen)||◈ Laminin|
|◈ Tenascin||◈ Collagen IV||◈ YKL‐40 (Chondrex)|
|◈ TIMPs||◈ Undulin|
|◈ TGF‐β||◈ MMPs|
4.1.2. Indirect marker and combined panels of liver fibrosis
Indirect markers of fibrosis are simple routine blood tests reflecting alterations in liver function but not directly representing ECM homeostasis. These biomarkers include indices related to portal hypertension (platelet count and spleen size), liver synthetic parameters (i.e., albumin), liver enzymes such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT) , AST/ALT ratio [124, 125], bilirubin, prothrombin index (PT) , γ‐glutamyl transferase (γ‐GT), and apolipoprotein A1(apo‐A1). They can be used in combination to produce sophisticated serological panels such as PGA index (prothrombin time, γ‐GT, and apo‐A1) [127–129] and APRI (AST to platelet ratio index) [130, 131]. PGA is one of the first biological indexes used for the noninvasive detection of cirrhosis in ALD patients . APRI is based on serum AST level and platelet . It is calculated as (AST/upper limit of normal*) × 100/platelet count and has been extensively studied in patients with HCV or ALD (*adjusted according to the reference values of each laboratory) [107, 132]. PGA index was subsequently modified to the PGAA index by the addition of α2‐macroglobulin which resulted in some improvement in its performance (PGAA) . Analysis of studies of indirect markers of fibrosis reveals several features, which are applicable to routine clinical practice. First, in viral and NAFLD, an AST/ALT ratio of greater than 1 is frequently associated with progressive liver fibrosis or cirrhosis [133–135]. Second, both components of the PGA index such as γ‐GT and thrombin index are markers of advanced liver fibrosis and can be used to discern patients with more advanced liver fibrosis. Indeed, the prothrombin index has been carried out alike or better than specific other markers of liver fibrosis [117, 136]. It should be emphasized that these markers represent liver dysfunction or structure rather than the disturbance of normal ECM metabolism (Table 6) .
|Direct serum markers||Indirect serum markers/combined panels|
|◈ HA||◈ Liver enzymes (ALT, AST)|
|◈ Laminin||◈ AST/ALT|
|◈ YKL‐40||◈ γ‐GT|
|◈ Procollagen type III||◈ Platelet count|
|◈ PIIINP||◈ Albumin|
|◈ MMP‐1 and ‐2||◈ Bilirubin|
|◈ TIPMs||◈ PGA|
|◈ TGF‐β||◈ APRI|
4.1.3. Indices/algorithms combining indirect and direct markers of liver fibrosis
The limitations of each marker to assess liver fibrosis have led to the development of more sophisticated algorithms or indices combining the results of panels of markers that substantially improved diagnostic accuracy in noninvasive evaluation of liver fibrosis (Table 7). In most studies, indices have been validated against the current clinical gold standard, liver biopsy, using as expression of their effectiveness the AUROC with optimal value being as close as possible . The first proposed index was based on a parented mathematical formula combining five variables (total bilirubin, γ‐GT, haptoglobin, α2‐macroglobulin, and apo‐A1)  and the results of this test were ranged from 0 to 1.0, using Fibrotest as a reference. In the initial report, a very low score (<0.1) allowed the exclusion of significant fibrosis with a 100% negative‐predictive value (NPV), whereas a moderate high score (>0.6) allowed the diagnosis of significant fibrosis with a 90% positive‐predictive value (PPV), using liver biopsy as a reference. Overall, liver biopsy could have been avoided in 46% of the patients from that study. Fibrotest has been primarily used for patients with chronic viral hepatitis and is now extensively evaluated in the patients with chronic hepatitis C [109, 138, 139] but also in other cases, such as hepatitis B [140, 141], HCV and HIV coinfection , NAFLD , ALD , and renal‐transplanted patients with chronic HCV . The recent meta‐analysis that pooled 7985 subjects (with analysis of individual data in 3282) with both Fibrotest and biopsy (HCV, 4600; HBV, 1580; NAFLD, 267; ALD, 524; mixed form, 1014) and the mean standardized AUROC for diagnosing significant fibrosis was 0.84 (95% confidence interval: 0.83–0.89), without differences between causes of liver disease. Therefore, Fibrotest have been used as an alternative to liver biopsy for the first‐line assessment of fibrosis and common chronic liver diseases, namely HCV, HBV, NAFLD, and ALD . One of the important issues of these algorithms is that in individual patients they cannot reliably differentiate the intermediate stages of fibrosis. Finally, in patients with chronic HCV, the application of these algorithms or indices can confirm or exclude fibrosis in less than 40% of patients .
|ViraHep C model |
|Fibrosis Probability Index (FPI) |
|Goteborg University Cirrhosis Index (GUCI) |
|Forns score |
|ELF score |
|BAAT score |
|BARD score |
|NAFLD fibrosis score [158, 159]|
|FIB‐4 score |
4.1.4. Combination of indices and algorithms for assessment of liver fibrosis
In order to increase diagnostic accuracy, new approaches using stepwise algorithms combining continually different indices have been proposed in patients with chronic hepatitis C  and B . For instance, one group was able to identify significant fibrosis with high diagnostic outcome above 94% diagnostic accuracy by APRI as screening procedure, followed by Fibrotest in APRI non‐classified cases and prohibiting liver biopsy to patients classified F0–F1 by noninvasive procedures. Cirrhosis could also have been recognized with 95% diagnostic accuracy applying a similar algorithm by the combination of APRI and Fibrotest (Figure 2). On the whole, liver biopsy could have been prevented in approximately 50 and 80% of patients for the diagnosis of severe fibrosis and cirrhosis in patients with chronic hepatitis C, respectively. Other groups have proposed alternative algorithms combining Fibrotest and APRI either with  or without Forns index . Otherwise, high diagnostic accuracy for the evaluation of significant fibrosis and cirrhosis has been reported for the combination of Fibrotest with Fibroscan that is based on the assessment of hepatic stiffness by TE [22, 109]. However, this method requires the availability of complex equipment, with limited access and costs that most likely exceed those of their more simple and accessible algorithms .
Several noninvasive markers of liver fibrosis have been represented but their application in substitute for liver biopsy may still remain controversy and is not generally acceptable due to still insufficient diagnostic performance. In fact, some of these methodologies such as APRI and Forns index remain in many cases unclassified group and all of them are not over 80–85% diagnostic performance [131, 139, 163, 164]. As a consequence, many patients still need to have a liver biopsy taken, and in those classified without liver biopsy, misdiagnosis is expected to occur in at least 15–20%, a figure that is considered inadequate by many clinicians [165, 166]. Most of them, such as APRI and Forns index, are not able to identify individual stages of fibrosis. APRI cannot be completely standardized due to the variability of measurement and normal ranges of AST in different laboratories . Since the diagnostic performance of described noninvasive markers is variable depending on the stage of fibrosis and other patients’ characteristics, they can be used to reduce rather than completely substitute the need for liver biopsy. Even though many studied have been shown that Fibrotest had the best performance when compared to other noninvasive methods, none of the investigated noninvasive markers of liver fibrosis has adequate accuracy for universal use instead of liver biopsy . And, one of the major critical points of the clinical application of serum markers and indices of liver fibrosis is that they are not regularly useful in most clinical situation. Another clinical point of these markers is that they are liver nonspecific and may be influenced by changes of their level; for example, HA levels increase after the meal  or in senile patients with chronic inflammatory states such as rheumatoid arthritis . Also, the repeatability of assessments of several biomarkers included in direct serum markers, such as AST levels or platelet count, is doubtful . The effect of serum lipid levels caused by anticholesteremic agents on the Forns index was taken into consideration. Finally, when applying Fibrotest in clinical situation, the evaluation should consider each of the five markers individually in order to escape false‐positive outcomes related to hemolysis (low hepatoglobin level), Gilbert syndrome (high bilirubin level), or false‐negative outcomes related to inflammatory reactions . However, a panel that combines proteins and proteinases of the ECM has been proposed and the results are promising . The combined use of some of these markers with the aim of reducing rather than completely abolishing liver biopsy may represent a rational and more convincing approach . In a large‐scale multicenter study, the diagnostic accuracy of a stepwise combination of two well‐studied noninvasive markers of fibrosis (APRI and Fibrotest) was followed by liver biopsy in only a subset of cases . This approach, called SAFE (sequential algorithm for fibrosis evaluation) biopsy, has been built up with double goal of detecting both severe fibrosis and cirrhosis and has here been confirmed to assure >90% diagnostic accuracy in comparison with respect to liver biopsy as the gold standard with <2% underestimation of the stage of liver disease as derived from NPV. The SAFE biopsy may be particularly useful for screening HCV‐infected patients in whom an immediate approach with liver biopsy is particularly problematic or questionable . Using two algorithms (Fibrotest and APRI), liver biopsy could be avoided in 50% of cases for the diagnosis of significant fibrosis and in 70% of cases for the identification of cirrhosis .
4.2. Imaging modalities and combinations with other markers for the diagnosis of liver fibrosis
4.2.1. Transient elastography (TE)
Liver fibrosis can be staged using one‐dimensional ultrasound TE (Fibroscan) , which is the most widely used imaging method for noninvasive and rapid measurement of hepatic tissue stiffness. Many studies have evaluated the diagnostic accuracy of TE for diagnosing cirrhosis with specificity and sensitivity approaching 90%. The accuracy for liver fibrosis detection is lower, with sensitivity and specificity approaching 70–80% [102, 175, 176]. Because both adipose tissue and the presence of fluid may influence the velocity of shear wave , obesity, ascites, acute inflammation, liver congestion, and elevated portal vein pressure may reduce TE accuracy. Furthermore, a falsely increased liver stiffness, due to postprandial increase in portal vein pressure, has been observed [177, 178]. Comparison of TE with biopsy results has provided that cut‐off values can be demonstrated to differentiate mild and moderate fibrosis from advanced fibrosis and cirrhosis, with validation tests showing variable performance and with greatest statistical significance being ensured in the distinction of cirrhosis from mild fibrosis (AUROC F = 4 (0.94), sensitivity F ≥ 2 (85%), specificity F ≥ 2 (91%)) [179, 180]. Investigations have applied various best stiffness cut‐off values, making comparison between researches. Generally, advanced fibrosis is more likely with higher cut‐off values (Table 8) [181, 182]. The optimal cut‐off value is 14.6 kPa for the detection of cirrhosis, but a cut‐off value of 10.0 and 14.1 kPa was adequate to achieve 95% sensitivity and specificity in their HCV patients with cirrhosis . Otherwise, the performance of TE was low for discriminating mild from significant liver fibrosis  and Spearman’s correlation coefficient between the elasticity scores using real‐time TE and histopathological fibrosis stage was low at 0.48 . However, TE was more useful for the identification of advanced fibrosis and their necroinflammatory activity influences TE measurements in patients without cirrhosis  and might be overestimated liver fibrosis when ALT is elevated . Some reports were shown that good correlation between TE and fibrosis exists, but data on TE in an Asian cohort show only 8% of patients having limited HCV . Liver stiffness measurement (LSM) by TE is a reliable predictor of liver fibrosis in Indian patients with chronic hepatitis C and B. LSM is superior to APRI for noninvasive diagnosis of hepatic fibrosis and cirrhosis, and high bilirubin (10.5 mg/dL) and Ishak HAI grade (>11) were independent predictors of discordance between liver biopsy and LSM . Liver stiffness has also been revealed to have good correlation with steatosis, necrotic inflammatory activity and hepatic iron accumulation as well as fibrosis . TE is restrictive, however, by its impossibility to perform in patients with ascites and patients with narrow intercostal spaces or morbid obesity. Advantages of TE include a short procedure time (<5 min), immediate results, and the ability to perform the test at the bedside or in an outpatient clinic.
|Etiologies||Patients (n)||Metavir score||Cut‐offs AUROC(kPa)||SE (%)||SP (%)||CC (%)|
|F ≥ 2 (%)||F 4 (%)|
4.2.2. Magnetic resonance elastography (MRE)
MRE is a noninvasive method of measuring the viscoelastic properties of the liver and evaluate liver stiffness by measuring the propagation of mechanical waves . MRE indicated that patients with hepatic fibrosis have higher LSM than normal volunteers  and that those with mild fibrosis were able to be distinguished from those with moderate or advanced fibrosis, with a mean hepatic shear elasticity being 2.24, 2.56, and 4.68 kPa in patients with F0–F1, F2–F3, and F4 fibrosis, respectively . MRE is superior to TE because of its ability to scan the whole organ and its application in patients with ascites or obesity. MRE was accurate in liver fibrosis staging and superior to biochemical testing with APRIs in patients with chronic HBV and HCV infection [197, 198]. These findings suggest that noninvasive MRE potentially has a role in determining the treatment and the prognosis of patients with chronic liver disease because it enables substantial and advanced fibrosis to be readily diagnosed. More particularly, MRE might be useful in the selection of patients with liver fibrosis who should either be treated (score of ≥F2) or undergo surveillance for portal hypertension and hepatocellular carcinoma (score of ≥F3) . Antiviral treatment should be considered in patients with liver stiffness values of ≥2.8 kPa . The main drawbacks are the high cost and complexity of the method that is too procrastinating for daily clinical practice. MRE values may be affected by the increased portal vein pressure following a meal similar to TE .
4.2.3. Acoustic radiation force impulses (ARFI)
ARFI use conventional hepatic ultrasonography to assess liver stiffness [199, 201]. ARFI uses short duration of acoustic pulses that produce mechanical excitation. The speed of the produced waves correlates directly with the extent of liver fibrosis and results are expressed in m/s. For fibrosis quantification, the “Virtual Touch (VT) tissue quantification” application was used, allowing for the measurement of SWV (shear wave velocity, m/s) within the interest area chosen by the examiner, according to principles. The higher the tissue stiffness shows, the higher the SWV produces . The theoretical advantage of ARFI as compared to TE is its implementation on an ultrasound device, via additional software imaging control and detection algorithms, thus allowing the visualization of B‐mode, color Doppler mode, and ARFI images with same equipment . Advantages of this technology include the ability to select the area to be assessed, avoiding large vessels or ribs  and the fact that steatosis does not influence the accuracy of the procedure. Otherwise, ARFI and TE are influenced by high ALT levels. In European patients with chronic hepatitis B and C, ALT values between 1.1x and 5xULN had only limited influence on ARFI values. The best cut‐off values for predicting significant fibrosis and cirrhosis were similar in patients with moderately elevated ALT levels .
4.2.4. Real‐time sonography‐based elastography (RTE)
RTE is a new method for the measurement of tissue elasticity different from TE. The echo signals are captured in the real time, while the probe slightly compresses or relaxes the body through freehand operation. Many clinical researches indicated that RTE could allow a high accuracy on the differential diagnosis of superficial focal pathological lesion such as mammary gland tumors, thyroid tumors, and prostate tumors [204, 205]. This method estimates the velocity of a shear wave through the liver using US and results are expressed in kPa. The diagnostic accuracies expressed as AUROC were 0.75 for the diagnosis of significant fibrosis (F ≥ 2), 0.73 for severe fibrosis (F ≥ 3), and 0.69 for cirrhosis. For a combined elasticity‐laboratory scores (platelet count and γ‐GT), AUROCs were 0.93, 0.95, and 0.91, respectively. Therefore, RTE is a new and promising sonography‐based noninvasive method for the assessment of liver fibrosis in patients with chronic viral hepatitis .
4.2.5. 2D‐Shear wave elastography (2D‐SWE)
2D‐SWE combines ultrasound images with radiation force induced into the liver. 2D‐SWE can measure shear waves propagation in real time . Advantages of 2D‐SWE (m/s or kPa) include good applicability and adjustable region of interest depending on the operator . Its failure rate is significantly lower than that of TE [206–208], particularly in patients with ascites [207, 208], but not in obese patients when the XL probe is used for TE (10.4 vs. 2.6%, respectively) . In a pilot study in 121 patients with chronic hepatitis C (Metavir, 41% F0/F1, 27% F2, 12% F3, and 20% F4), AUROCs of 2D‐AWE for the diagnosis of significant fibrosis and cirrhosis were 0.92 and 0.98, respectively . Sensitivities and specificities were 85 and 92% for the diagnosis of significant fibrosis using a cut‐off of 7.1 kPa, and 97 and 93% for the diagnosis of liver cirrhosis using a cut‐off of 10.1 kPa. Therefore, 2D‐SWE is a promising technique that is currently under investigation. It seems to be at least equivalent to TE and pSWE/ARFI for noninvasive staging of liver fibrosis in viral hepatitis .
4.2.6. Sonography‐based imaging
US imaging has been used to noninvasively evaluate the severity of liver fibrosis in patients with chronic HCV. Results vary with some studies showing associations between US score and diagnosis of cirrhosis with various sensitivities (87.5–100%) and specificities (81.5–93.5%) [210, 211]. The application of US to assess liver fibrosis was used by calculating a fibrosis extraction ratio (FER) (fiber volume/total volume), which was able to distinguish F0/F1 from ≥F2 fibrosis with a sensitivity of 55% in the HCV cohort . In sonography, contrast‐enhanced sonography is based on intravenous injection of specifically sized microbubbles, transferred with a shell of protein or biopolymers that facilitate their sonographic imaging . Some report studied the hepatic vein transit time (HVTT) for grading liver disease using a microsound microbubble contrast agent as a tracer. This study also applied Doppler sonography to make a decision for several indices to assess portal vein congestive index, but found that there was no significance. HVTT was significantly shorter in cirrhotic patients than in non‐cirrhotic patients (p < 0.001) and distinguished between these patients with high accuracy . Therefore, unenhanced Doppler ultrasound is not reliable in the discrimination of varying degrees of fibrosis, but that results can be improved with additional measurement such as heart pulsation at the liver surface and portal venous flow measurements. Color Doppler is a noninvasive method for assessing portal hemodynamics. In the study for portal hemodynamics by color Doppler and gastric mucosal blood flow (GMBF) by laser Doppler velocimetry in patients with cirrhosis, portal venous blood flow (PVBF), portal flow velocity (PFV), and GMBF were all significantly slower in cirrhotic patients and PVBF and PFV were lower in Child’s class B/C than in class A . A statistically significant difference has been shown in all US markers between patients with and without cirrhosis, but sensitivity and specificity were significantly increased when evaluation of the transmission of heart pulses on the liver surface area included as part of the US test a sensitivity of 85 versus 55% and a specificity of 93 versus 86%, respectively .
4.2.7. Per rectum TI‐201 scintigraphy (TI‐201 test)
A complete understanding of the hepatic disease requires the evaluation of portal circulation, which allows for more appropriate treatment and follow‐up of patients. During the last six decades or more, several clinical reports have investigated portal circulation by radioactive tracers [87, 88]. These reports have been established that TI‐201 test allows us to understand the portal circulation, and a new method using TI‐201 distribution patterns seems to be useful in evaluating the portosystemic shunt (heart/liver uptake ratio, H/L ratio), which can develop to varying extents in liver cirrhosis and positive correlation to portal pressure in patients with chronic hepatitis [87–89, 217]. Our previous studies on the clinical value of H/L ratio in chronic liver disease may be useful in differentiating chronic hepatitis from cirrhosis and the prediction of its prognosis for the management of disease . Noninvasive test such as maximal removal rate of indocyanine green and H/L ratio, as well as ALT/AST ratio, prothrombin time, and platelet count, may be used to evaluate the progression of chronic liver disease without liver biopsy  as well as progression of variceal bleeding without an endoscopy in biopsy‐proven patients with cirrhosis . However, because most serum markers except H/L ratio may be changeable by medical treatment of chronic liver disease, serum markers are not suitable for monitoring long‐term outcomes of patients with cirrhosis. On assessing the predictive values of H/L ratio for decompensation during the follow‐up period of 45.5 months in 107 patients , the last visiting value of H/L ratio provided a strongly reliable predictor of decompensation with an odds ratio estimate of 14.4, an AUROC of 0.825, a cut‐off of 0.4, a sensitivity of 73.1%, and a specificity of 71.6% (Figure 3).
5. Conclusion and perspectives
There is an urgent need to pursue the development of noninvasive tests in addition to a liver biopsy for the staging of fibrosis. The area of liver fibrosis and cirrhosis has been extensively studied during the few decades. As a result of growing understanding of liver injury and fibrosis, a number of noninvasive tests for fibrosis that are accurate and replace liver biopsy are being used to develop, commercialized, and are being used more and more in practices. The current serum tests are a start and may have utility in identifying patients with minimal fibrosis who do not require a liver biopsy. Because of the conditional relationship with biopsy, the development of serum markers will always have obvious limitations. The use of noninvasive tools varies widely depending on practice setting and the individual physician’s management style. However, as with many new diagnostic methodologies, such tests are being adopted and marketed while the evidence of their general usefulness in various clinical settings remains incomplete. For instance, there is no solid evidence that the currently available tests for liver fibrosis have the precision necessary for tracing disease progression in real time or patient’s response to therapy. Before such tests are accepted, their superiority to routine laboratory studies should be demonstrated. Although invasive liver biopsy is still the gold standard to assess the nature and severity of hepatic fibrosis, it has several recognized limitations including sampling error and inter‐observer variability in interpretation and staging. Furthermore, the dynamic process of fibrosis resulting from progression and regression is difficult to capture with biopsy alone. Therefore, alternative, simple, reliable, and noninvasive direct and indirect serum markers able to predict the presence of significant fibrosis or cirrhosis in patients with chronic liver disease with considerable accuracy were needed. The hepatology experts are actively researching noninvasive methods of fibrosis quantification. This chapter reviewed the nature and limitations of the several noninvasive methods for the assessment of the presence and severity of liver fibrosis in patients with chronic liver disease.