Studies on Infectious Etiologies of Canine Chronic Renal Failure with Emphasis on Diagnostic Biomarkers

Abstract

Ongoing renal disappointment results from a moderate and irreversible loss of working of nephrons, and the reason is frequently hard to determine. The reasons for renal disappointment can be intrinsic or extrinsic. Extrinsic incorporates cardiovascular sickness, over weight, diabetes, sepsis and respiratory and hepatic disappointment. Intrinsic causes incorporate glomerular nephritis, polycystic renal illness, renal fibrosis, tubular cell death and stones. Common aetiology identified As: Bacteria (Lyme borelliosis, urinary tract infection, Leptospira), Viruses (canine adenovirus), Hemoprotozoan and Rickettsia (Leishmania infantum, Ehrlichia canis, Anaplasma platysine, Babesia canis vogeli, Hepatozoan canis) or dietary (proteins rich in sulphur-containing amino acids). Serum biomarkers like SDMA, ADMA, NGAL and Cystatin-c are of much diagnostic aid, that even 25% of renal insult can be identified.

1. Introduction

Renal failure is the loss of ability of kidneys to excrete wastes, concentrate urine, conserve electrolytes and maintain fluid balance. It is of two types, acute renal failure (ARF) or acute kidney injury (AKI) and chronic renal failure (CRF) or chronic kidney disease (CKD) [1]. Renal failure is the major cause of death in young and older dogs. 15% prevalence for renal failure has been observed in dogs over 10 years of age and up to 31% in cats over 15 years of age [2].

Acute kidney injury (AKI) is characterised by sudden decrease in renal filtration resulting in high levels of serum creatinine, acute uraemia and decrease in the volume of urine. AKI affects humans, dogs and cats, which may result from one or more contributing causes and it may differ in severity [3]. Nephrotoxins and ischemia are the most common causes of renal diseases in dogs. Common nephrotoxicants are aminoglycosides, vitamin D, nonsteroidal anti-inflammatory drugs, lilies, raisins, grapes, etc. [4]. Ischemia usually occurs due to shock, dehydration, decreased cardiac output, renal vasculature thrombosis and hypotension. Major infectious causes of acute renal failure are leptospirosis, ehrlichiosis, babesiosis and pyelonephritis [5].

Mild AKI generally goes unnoticed and generally recognised in advanced stages and is clinically characterised by anorexia, depression, oral ulceration, vomiting and/or diarrhoea, or oliguria. Chronic kidney disease (CKD) is due to loss of functional renal tissue due to a prolonged (≥2 months), usually progressive, process. CKD often smoulders for many months or years before it becomes clinically apparent, and it is invariably irreversible and frequently progressive. Because AKI may progress to a chronic condition, any cause of AKI is also a possible cause of CKD. CKD should be distinguished from the more readily reversible acute disease by history, physical examination and laboratory findings, although a renal biopsy may be required [6].

Chronic renal failure results from a progressive and irreversible loss of functioning of nephrons, and the cause is often difficult to determine. CRF in dogs is characterised by polyuria, polydipsia, anorexia, diarrhoea, weight loss, pallor mucous membrane, oral ulceration, halitosis, acute blindness, etc. CRF is caused by several risk factors including old age, diverse breeds, small body size, peridontal disease, obesity, etc. [7]. Kidney disease which is present for 3 months or longer can be regarded as chronic. The duration of CKD can be determined from medical records or can be assessed by physical examination or renal structural changes by imaging or renal pathology [2].

CKD is generally classified into 1 to 4 stages. Generally, no clinical signs are seen until ≥75% of nephron function has been impaired (Stages 3 and 4). In Stage 1, a process is damaging the kidneys but azotemia and clinical signs have not developed. In Stage 2, the disease has progressed, GFR has fallen to <25% of normal, and azotemia is present, but clinical signs are not yet seen but there may be impaired urine-concentrating ability and increased urine volume. In stage 3, GFR has declined further, azotemia is present, and clinical signs are often seen. In stage 4, there is severe azotemia with clinical signs. Usually, the earliest clinical signs in CKD are polydipsia and polyuria (late Stage 2 or early Stage 3). In Stages 1 and 2 of CKD, diagnosis is often missed or made incidentally. In Stages 3 and 4, the BUN, serum creatinine, and Pi are increased and K is generally decreased. However, hyperkalemia may be associated with oliguria and anuria. The urine specific gravity may range from 1.001 to 1.060 in dogs. In animals with dehydration and normal renal function, it should be >1.030. The inability to produce concentrated urine in dehydration is an early sign of CKD but concentrated urine is rarely seen when the serum creatinine is >4 mg/dL in an animal with azotemia of renal origin [6].

The complete history, physical examination, urinalysis, haematology, serum biochemistry, and nephrosonography provide a realistic way to diagnose CRF in dog. Early diagnosis, systematic approach to CRF diagnosis and therapeutic management can delay the progression of illnesses in dogs [2].

Serum creatinine is considered as the diagnostic tool for detecting renal failure but it has certain drawbacks such as low sensitivity and low specificity during early disease and is affected by muscle mass. Recently, novel serum and urine biomarkers have been reported which have been found to be more specific and sensitive indicators to diagnose both ARF and CKD in human and veterinary patients. These biomarkers can differentiate different processes such as glomerular damage, reduced GFR and tubular dysfunction that lead to renal disorders [8].

Some markers can be used in the detection of glomerular or tubular dysfunction earlier than conventional methods. An ideal biomarker should be specific, non-invasive, sensitive to allow early detection, specific of the extent/severity of disease, be suitable for monitoring progression, informative w.r.t. the localization of the injury and the clinical outcome, inexpensive and readily available from a reference laboratory [9, 10]. Protein markers of tubular function damage and dysfunction e.g. retinol binding protein (RBP), neutrophil gelatinase-associated lipocalin (NGAL), Kidney Injury Molecule 1 (KIM-1) and enzymes can be markedly increased in the urine due to reduced tubular reabsorption [11].

For early detection and more specific and sensitive diagnostic capability in renal diseases, novel serum and urine biomarkers are being tested in both human and veterinary patients. An ideal biomarker is that which is specific for the detection of kidney disease (both AKI and CKD), sensitive for detecting early disease, non-invasive, low cost, able to monitor disease progression, reveal injury location and severity of disease and predict clinical outcome [8]. Asymmetric Dimethylarginine (ADMA) is an endogenously generated methylated arginine that has been associated with endothelial dysfunction and kidney damage. Symmetric Dimethylarginine (SDMA) concentration is highly correlated with inulin and creatinine clearance in man with CKD. Kidney Injury Molecule-1 (KIM) concentration is highly specific for detection of proximal tubular injury in kidneys and is used primarily to detect AKI. Cystatin C is freely filtered at the glomerulus and is absorbed and catabolised in proximal tubule cells with decreased tubular secretion [12].

2. Etiopathogenesis

The glomerulus is interposed inside the renal cortex, between an afferent and efferent arteriole, and is the source of water filtration and blood solutes. This filtrate travels through the space of Bowman, and is then significantly altered as it passes through the renal tubule. The functions of the different segments of the renal tubule are expressed in the epithelial cells which line the tubule’s having functional and structural specialisations [13].

Major function of kidney is to maintain homeostasis of body i.e. regulation of electrolyte & acid-base balance, water balance, arterial blood pressure and excretion of metabolic wastes, hormone and exogenous compounds (e.g. drugs). It synthesises erythropoietin and active vitamin D. It helps in gluconeogenesis during fasting. The juxtaglomerular cell produces the hormone renin in response to reduced circulating volume to kidneys. The renin plays an important role in sodium, extracellular fluid volume, and blood pressure homeostasis [14].

The glomerular basement membrane serves as a filtration barrier between the bloodstream and tubular lumen of nephrons. Plasma flowing through glomerular capillaries is filtered into the Bowman’s space. The glomerular filtration barrier allows all free proteins of molecular weight lower than approximately 30 kDa and radius lower than 20 Å [15]. Glucose and amino acids, such as cystine, ornithine, lysine and arginine are almost completely reabsorbed in the proximal tubule [16].

The mechanism responsible for acute increase in renal blood flow and GFR is responsible for continuous hyper filtration and accompanying renal hypertrophy due to long-term protein intake [17]. The renal cortex receives 90% of the renal blood flow and contains the large endothelial surface area of the glomerular capillaries which is susceptible to blood-borne toxicant exposure. In the renal cortex, the epithelial cells of proximal tubule and thick ascending loop of Henle are most affected by ischemic and toxicant-induced injury [18].

Chronic kidney disease (CKD) has been defined and classified in various ways over time, but current international guidelines define it as decreased kidney function manifested by the glomerular filtration rate (GFR) of less than 60 mL/min per 1.73 sq.m [19].

The major pathophysiologic mechanisms contributing in CRF includes decreased renal perfusion pressure, decreased filtration coefficient, high intratubular pressure, acute tubular necrosis (ATN), interstitial nephritis and interstitial oedema [20]. ATN is caused by a variety of factors, including pre-renal azotemia, urinary tract obstruction, vasculitis, glomerulonephritis and acute interstitial nephritis, leading to acute renal failure. However, ischemic or toxic ATN is the leading cause of acute renal failure [21].

Deposition of amyloid (protein) in glomeruli, blood vessels and cortical tubules is the cause of proteinuria leading to chronic renal failure. Primary amyloidosis is associated with osteolytic multiple myeloma and the development of nodules in organs. Secondary amyloidosis is associated with persistent infections [22]. Chronic renal failure has been occasionally associated with hypercalcemia in dogs and cats. In patients with chronic renal failure, the combination of hyperphosphatemia, decreased renal calcitriol output, and decreased plasma ionised calcium concentrations promotes PTH secretion in an attempt to preserve normal calcium homeostasis [23]. Progression to chronic renal disease is linked to etiologies that cause glomerular hypertension, elevated systemic hypertension and chronic interstitial nephritis [24].

Proximal tubular cell reabsorbing proteins from the tubular fluid leads to the possibility that proteins or associated molecules adversely affect the biological status of the tubular cell leading to proteinuria [25]. Long continued proteinuria can lead to permanent structural changes in the nephron leading to impaired renal function. Erythropoietin is derived from peritubular interstitial cells in the renal cortex and the outer renal medulla in the kidneys. The lack of renal erythropoietin leads to anaemia in chronic interstitial nephritis [26]. Heiene et al. [27] studied renal histomorphology in dogs with Pyometra and long-term clinical outcome with respect to signs of renal disease and concluded that Pyometra is one of the causes of renal disorders in canines. Endotoxin generated in the uterus due to pathogenic bacteria reach the kidney via systemic circulation and cause interstitial inflammation and tubular atrophy leading to nephritis and renal failure.

Mishinam and Watanabe [28] concluded that the activation of the rennin angiotensin aldosterone system in chronic renal failure causes hypertension in dogs and attributed this to loss of functional nephrons. Grauer [29] stated that the pathophysiology of CKD could be regarded at both the organ and systemic levels. At the level of the kidneys, the main pathology of CKD was loss of nephrons and decreased glomerular filtration which leads to increased plasma concentration of substances that are normally cleared by renal excretion. Chew et al. [30] stated that intraglomerular hypertension and hyper filtration were compensatory mechanisms leading to the progression of CKD. Hyper filtration primarily results from increased glomerular ultrafiltration coefficient (Kf) and increased Trans glomerular capillary pressure. Proteinuria and glomerulosclerosis are consequences of this hyper-filtration [31].

CKD includes diseases of the macrovascular compartment (such as systemic hypertension, coagulopathy and chronic hypoperfusion), microvascular compartment (such as systemic and glomerular hypertension), interstitial compartment (such as pyelonephritis, neoplasia, obstructive uropathy, allergic and immune- nephritis) glomerulonephritis, developmental disorders, congenital collagen defects and amyloidosis [32]. Prostaglandins play a role in the kidney, such as control of renal blood flow, glomerular filtration, renin release and sodium excretion. NSAIDs interfer with prostaglandin production and lead to disease progression [33].

CKD aetiology is largely unknown as it is thought to be due to various causes including oxidative stress, inflammation, cardiac and endothelial dysfunction, metabolic disorders other than primary renal dysfunction [34].

The disease tends to progress in dogs with IRIS CKD Stages 3 and 4. The majority of dogs with this severe CKD will die or be euthanized as a result of their illness [35].

Dogs with IRIS CKD Stages 3 and 4 normally live for few months to a year or two, depending on the severity of their kidney disease, but with early diagnosis and thus successful treatment, survival periods may be significantly increased [36].

The presence or absence of kidney damage, urine output, hypertension and changes in GFR are all key factors determining the prognosis as well as course of the disease in dogs [37].

3. Prevalence

3.1 World wide

Sosnar et al. [38] studied 1099 cases admitted between 1990 and 2001 to the University of Veterinary and Pharmaceutical Science, Brno and recorded 139 cases (111 dogs & 28 cats) of renal failure with prevalence of 12.7%. O’Neill et al. [39] reported the apparent prevalence of chronic kidney disease of 0.21% and total prevalence of 0.37% in a merged clinical database of 107,214 dogs attended at 89 UK veterinary practices over a 2-year period (January 2010–December 2011).

3.2 Aetiology

Camacho et al. [40] reported 36% (21/58) dogs prevalence of azotemic with case fatality of 22% amongst UTI cases. Brown et al. [6] reported melamine and cyanuric acid pet food–associated renal failure affecting 16 animals in 2 different outbreaks. In a 5 year clinical study, Yhee et al. [41] reported prevalence of renal diseases such as glomerular disease (22.9%), tubulointerstitial disease (8.6%), neoplastic disease (8.6%), conditions secondary to urinary obstruction (24.3%) and other diseases (35.7%). Mshelbwala et al. [42] in a study between 2012 and 2015 reported 22.81% prevelance of glomerulonephritis. Out of these acute cases of glomerular and interstitial nephritis were mostly associated with leptospirosis (70%), colibacillosis (10%), other bacteria (15%) and unidentified causes (5%), whereas chronic cases were mostly associated with long standing cases of leptospirosis (70%), trypanosomosis (10%), babesiosis (10%) and unidentified causes (10%). Valentina et al. [43] reported 56% prevalence of Ochratoxin-toxicity in dogs leading to chronic renal failure.

4. Breed

Osborne et al. [44] documented congenital renal disease in more than 30 breeds of dogs such as German shepherd, Doberman, Great Dane, Lhasa apso and Boxer. Gabriel [45] recorded that Labradors were the most affected (46.42%) breed in renal failure, followed by German shepherd (32.14%), Spitz (14.28%), Cocker Spaniel (3.51%) and Saint Bernard (3.51%).

5. Age

Rubin [46] reported that CRF occurs in dogs and cats of all ages and is common disease in older animals as there was increase in incidence of CRF with age. The mean age of CRF dogs was 7 years in dogs and it was 7.4 years age in cats. Paul et al. [47] concluded that the chronic kidney disease in dogs occurred at an average age of 9.9 years and 15 years in cats. Tarafder and Samad [48] in a case control study of 3670 sick pet dogs reported 48.12% prevalence of renal failure in age group above 36 months. Main causes were babesiosis (0.08%), sinusitis (0.08%), nephritis (0.19%), poisoning (0.33%), urinary tract infection (2.10%) and haematuria (2.34%).

Nabi et al. [49] observed higher prevalence of renal disease in dogs over ten years of age. Highest prevalence of 44.28 percent has been recorded in age range of 5–10 years followed by dogs older than 10 years (40.96%) and lowest prevalence in dogs aged 5 years (14.76%) [50].

6. Classification

6.1 IRIS staging of chronic kidney disease (CKD)

IRIS CKD staging is based on fasting blood creatinine concentration and blood SDMA concentration. SDMA is considered as more sensitive marker. The diagnosis of chronic kidney disease (CKD) is undertaken to promote adequate care and monitoring of canine or feline patients.

In stage 1, (non-azotemic) with normal blood creatinine (<125 μmol/l or < 1.4 mg/dl) or normal (<18 g/dl) or mild increase blood SDMA. Subsequently, increasing blood SDMA concentration (>14 μg/dl) may be used for early CKD diagnosis. The other renal abnormality must be checked such as decreased urinary concentrating ability without identifiable non-renal cause, abnormal renal palpation or renal imaging findings, proteinuria of renal origin, abnormal renal biopsy results or increasing blood creatinine or SDMA concentrations in preceding samples.

1. In stage 2, (mild renal azotemia) with normal or mildly elevated blood creatinine (125-150 μmol/l or 1.4–1.8 mg/dl) or mild elevated blood SDMA (18-35 g/dl). The clinical signs are usually mild or absent.

2. In stage 3, with moderate renal azotemia and elevated blood creatinine (251-440 μmol/l or 2.9–5 mg/dl) or elevated blood SDMA (36–53 ug/dl). Many extra renal signs may be seen, but their extent and severity may vary. If signs are absent, the case could be considered as early Stage 3, while presence of marked systemic signs justifies classification as late Stage 3.

3. The stage 4, by elevated blood creatinine (>440 μmol/l or > 5 mg/dl) or elevated blood SDMA (>54 μg/dl) with the increasing risk of systemic clinical signs and uremic conditions.

6.2 IRIS grading of UP:UC

The magnitude of protein loss in urine is interpreted by the quantity of protein excreted in urine in comparison to quantity of creatinine excreted in urine (UPC). The IRIS classification of proteinuria in CKD is divided in sub stages as proteinuric (UPC > 0.5), borderline (UPC 0.2–0.5) and non proteinuric (UPC <0.2). The proteinuric stage has worse prognosis with shorter survival time than other stages [51].

6.3 IRIS grading of blood pressure

The IRIS classification of systolic blood pressure (SBP) is based on the risk of future target organ damage i.e.: (i) Normotensive (<140 SBP) at minimal risk; (ii) Prehypertensive (140–159 SBP) at low risk; (iii) Hypertensive (160–179 SBP) at moderate risk; (iv) Severely hypertensive (>180 SBP) at high risk.

7. Aetiology

The cause of renal failure can be intrinsic or extrinsic. Extrinsic factors include cardiovascular disease, obesity, diabetes, sepsis and pulmonary & hepatic failure. Intrinsic causes include glomerular nephritis, polycystic renal disease, renal fibrosis, tubular cell death and stones [52].

Legatti et al. [3] reported 29.4% prevalence of infectious aetiology in ARF in dogs, which includes leptospirosis (43.6%), pyelonephritis (5.7%), pyometra (37.4%), sepsis (2.5%) and non-infectious aetiology (60.4%), which further included nephrotoxic (30.3%), obstructive (30.3%) and unknown aetiology (36.5%).

7.1 Bacteria

Dambach et al. [53] reported 18 positive cases of Lyme borelliosis in lyme endemic area leading to nephritis in dogs. Martinez et al. [54] reported 17 dogs with polypoid cystitis with clinical presentation of hematuria and recurrent urinary tract infection (UTI). Proteus species (23.1%) was the most common bacteria isolated on urine culture. Other isolated organisms were Escherichia coli, Staphylococcus and Enterococcus species. Hutton et al. [55] reported Weissella viridescens, Shigella sonnei, Clostridium perfringens, and E. coli in the renal tissue.

7.2 Leptospira

Urinalysis from dogs with leptospirosis is reported for isosthenuria and in rare cases hyposthenia while glycosuria and proteinuria were common observations [56]. Hepatic dysfunction along with azotemia characterised by increases in serum ALT, AST and ALKP and total bilirubin with electrolyte imbalance are indicative of suspicion of leptospirosis.

7.3 Viruses

Vright et al. [57] experimentally demonstrated proliferative glomerulonephritis with localization of IgG, C3 and viral antigen in mesangial in kidney after a trial of intravenous dose of canine adenovirus.

7.4 Hemoprotozoan and rickettsia

Poli et al. [58] in a prospective survey reported 413 dogs affected by naturally acquired Leishmania infantum infection out of which 34 dogs showed presence of glomerular lesions. Out of these, one group showed the mesangial-cell proliferation with focal features in 11 dogs and diffuse pattern in 10 dogs. The second group of 12 dogs showed the typical findings of segmental membrano-proliferative glumeronephritis and one dog showed the amyloid deposits in the glomerular tuft and interstitial.

Chronic ehrlichiosis caused by Ehrlichia canis was suspected to be the cause of the dog’s renal amyloidosis with development of proteinuria and renal failure, suggesting the presence of glomerulopathy [59]. Ferreira et al. [60] performed a comparative study between morphological and molecular tests for the diagnosis of Anaplasma platys infection in dogs in Brazil. The overall prevalence of A. platysine anaplasmosis in dogs was found to be 14.85% and 15.84% on basis of blood smear and PCR, respectively. Yabsley et al. [61] reported several tick-borne pathogens which were identified by serology and PCR. These included E. canis (24.7%), A. platys (19.2), Babesia canis vogeli (7%), Hepatozoa canis (7%) and Bartonella sp. (1.4%).

Tarafder and Samad [48] carried out a case control study to ascertain the prevalence of clinical diseases in 3670 sick pet dogs and reported 00.08% overall prevalence of babesiosis. Age-wise prevalence was higher in dogs above 36 months of age (00.05%) as compared to dogs between 7 to 36 months of age (00.03%). The haemogram showed mild anaemia and neutrophilic leucocytosis. Serum biochemical analysis showed a rise in ALP, ALT, globulin, BUN and creatinine and a reduction in total protein and albumin.

7.5 Urolithiasis

Urolithiasis is a frequent ailment that causes lower urinary tract disease in dogs and cats. The production of bladder stones is linked to the precipitation and crystallisation of a varied range of minerals like magnesium ammonium phosphate hexahydrate, calcium oxalate, urates, etc. Over the last 15 years, ureterolithiasis has emerged as a significant cause of acute and chronic renal illness in cats and dogs [62].

Calcium oxalate is the most prevalent component of upper urinary tract stones in dogs and cats with more than 90% of analysed nephrolith and urethrolith being CaO [63]. Because of a variety of anatomic factors, urethral blockage by uroliths is more common in male dogs than in female dogs. A smaller relative urethral diameter and longer urethral length, the curving path of the urethra around the ischium, and the existence of the os-penis, which limits urethral diameter expansion. Uroliths are most commonly found lodged at the ischial arch or immediately proximal to the os-penis in male dogs.

7.6 Neoplasms of urinary system

Transitional cell carcinoma (TCC) of the urinary bladder is one of the most prevalent neoplasms of the canine urinary system, accounting for 1.5–2.0 percent of all canine malignancies. TCC is typically an aggressive, and ultimately lethal cancer, with death due to post-renal blockage occurring within 3–12 months of diagnosis [64].

7.7 Fungal

Jin and Lin [65] retrospectively analysed 35 animals (23 dogs, 12 cats) affected by fungal urinary tract infections (UTIs) and identified 7 species of fungi in the affected animals. Candida albicans was the most common isolate. The common preceding diseases identified in affected animals were lower urinary tract diseases, diabetes mellitus, neoplasia and renal failure. Ahn et al. [66] reported renal failure related to ochratoxin A (OTA) and citrinin toxicity in 5 dogs referred to the Veterinary Medical Teaching Hospital at Kangwon National University with a common history of feeding pedigree dry dog food.

7.8 Role of diet

Dietary proteins of animal origin and proteins rich in sulphur-containing amino acids promote metabolic acidosis while vegetable proteins do not generally show this effect. Hence, marked restriction of dietary protein and decrease in phosphorus intake limits the renal ammoniagenesis [67].

Brown et al. [68] reported the supplementation with omega-6 polyunsaturated fatty acids (PUFA’s) pace the decline of kidney function, and omega-3 polyunsaturated fatty acids (PUFA’s) are Reno protective in nature.

The study on significance of clinical nutrition in geriatric dogs and cats suffering from chronic renal failure revealed that the renal diets used often have subtle protein, phosphorus and sodium content. The different dietary modifications such as subtle protein restriction, reduction in phosphorus and increase in the quantity of Omega 3 polyunsaturated fatty acids will aid in management and increasing the life span of the patient. The goal of nutritional treatment for dogs and cats affected by chronic renal disorders is to improve the quality and length of life, ensuring an adequate amount of energy and slow down the progression of renal failure [69]. Hyperkalaemia may be associated with commercial renal diets and it is a potential complication of CKD also. In CKD dogs, the formulated low potassium diets are effective for hyperkalaemia correction in renal failure.

8. Clinical signs

Mazzaferro et al. [70] reported oliguria or anuria and vomition after the ingestion of raisins or grapes in dogs. Jin and Lin [65] reported dysuria, haematuria, polyuria, anorexia, depression, and pyrexia as the most common clinical signs in dogs and cats affected with fungal urinary tract infections (UTI’s). Grauer [29] stated that reduced erythropoietin production contributes to non-regenerative anaemia in CKD and decreased metabolism and excretion of parathyroid hormone and gastrin contributes to osteodystrophy and gastritis, respectively. Parathyroid gland hyperplasia and subsequent hyperparathyroidism may occur secondary to chronic renal failure in dog. Renal secondary hyperparathyroidism triggers changes in circulating levels of calcium, PTH, phosphorus and 1, 25-dihydroxycholecalciferol. The increased PTH level can have deleterious effects including soft tissue mineralisation, fibrous osteodystrophy, bone marrow suppression, urolithiasis and neuropathy.

Oburai et al. [7] noted anorexia, vomiting, weight loss, dullness, oral ulcers, polyuria/polydipsia, hypertension (SAP>150 mmHg), Malena, pallor mucous membrane, recumbency and blindness in 31 dogs suffering from chronic renal failure.

Sosnar et al. [38] stated that up to 67 percent loss of renal function, animal remains clinically asymptomatic and that with 67–75 percent loss of renal function there may polyuria and polydipsia and that loss of 75–95 percent of renal function would be manifested as vomiting, diarrhoea, apathy and when less than 10% of renal function is left, signs may be accompanied along with encephalopathy.

Grauer [31] claimed that acute renal failure in canines was accompanied with inflamed kidneys, hemconcentration, metabolic acidosis, increased urinary sedimentation, marked hyperkalemia and renal pathological.

Pugliese et al. [69] stated that severe polydipsia and polyuria occurs with a loss of 67–75 percent of the filtration rate, when renal failure further progress’s (75–90%), the accumulation of blood nitrogen catabolic products determined the occurrence of systemic signs such as anorexia, weight loss and specific signs such as vomiting and diarrhoea. When the residual renal function was found to be less than 10%, uremia was present along with neurological manifestations (uremic encephalopathy) indicating the terminal stage of illness. Other signs of deteriorating renal function include polyuria/polydipsia, dehydration, electrolyte imbalances, acidosis, anaemia, systemic hypertension and renal secondary hyperparathyroidism [2].

Klosterman et al. [71] reported that a history of prolonged anorexia, vomiting, diarrhoea, weight loss, or a combination of these factors, polyuria/polydipsia (PU/PD) and nocturia were more frequent in CRF. For whatever magnitude of azotemia, clinical symptoms were more severe in animals with ARF than in CRF. Emaciation, poor coat quality and mucous membrane pallor were more prevalent in CRF than in ARF.

9. Diagnosis

9.1 Haematological

Fiocchi et al. [72] reported different haematological parameters viz. PCV (20 ± 4.1%), MCV (67.8 ± 7.0 fL), MCHC (33.9 ± 1.6 g/dL), Absolute reticulocyte count (20.7x10⁶/μL) and Platelet count (440 ± 242x10³/μL) in 33 dogs with renal disease. Torres et al. [73] reported normocytic normochromic anaemia in 84.1% of the dogs with CKD with no reduction in mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC), while other blood parameters declined.

Sumit et al. [74] in a study on 30 dogs with CKD observed lower mean values of haemoglobin (9.15 ± 0.67 g/dl), TEC (4.47 ± 0.30x10⁶/mm³), PCV (29.22 ± 2.05%) and platelet counts (196.23 ± 18.31x10³/μL) in all affected dogs. The TLC and lymphocyte count are reportedly higher than reference values. Anaemia is a risk factor for mortality in CKD dogs. Anaemia is not only a consequence of CKD but also a risk to healthy patients to CKD progression and further to End Stage Renal Disease [75].

Erythropoietin is produced by the peritubular interstitial cells of the inner cortex and outer medullary cells of the kidney. As the kidney disease progresses, there are less erythropoietin-producing cells within the kidneys, hence anaemia is evident [76].

Dorgalaleh et al. [77] revealed RBC, Hb, HCT and MCHC levels were significantly lower in AKI affected patients along with anaemia and thrombocytopenia.

9.2 Biochemical parameters

In a study on renal failure due to Babesia infection, the azotemic dogs had showed significantly lower concentrations of total protein, albumin, β and γ globulins while significantly higher values of α-2 globulin. The azotemic dogs have comparatively higher concentrations of cholesterol and triglycerides which may be as a result of compensatory mechanism of liver to the loss of proteins [40].

CKD patients having hyperlipidaemia pathogenesis can represent significant risk factors for accelerated atherosclerosis. CKD has also been associated with insulin resistance and glucose uptake. Cortadellas et al. [78] reported that hyperphosphatemia leads to CKD progression. The detrimental effect of phosphorus retention leads to secondary renal hyperparathyroidism, which had adverse effects on bones, kidneys, brain, heart, pancreas, muscle tissue, lungs, erythrocytes, lymphocytes, adrenal glands and testicles. Phosphorus retention eased the formation of calcium phosphorus (Ca-P) complexes that precipitated in the renal interstitial tissue and resulted in interstitial fibrosis and atrophy of the renal tubules, elevated urine protein to creatinine ratio (UP/UC ratio), increase excretion of ALP and GGT in urine, azotemia, hypercretenimia, hyperphosphatemia, hypernatremia with normal serum potassium and calcium level in renal failure dogs. Qurollo et al. [79] reported with IMHA, proteinuria, neutrophilia, abnormal lymphocytes and increased liver enzyme activity as common haemato-biochemical changes in renal failure dogs infected with Ehrlichia sp.

Adin and Cowgill [80] concluded that Leptospira interrogans in dogs often induces a hepatorenal syndrome defined by an acute onset of haemorrhagic diathesis, sub-acute icterus, or sub-acute uraemia followed by oliguria or anuria. Out of 37 dogs affected by leptospirosis, 17 of had neutrophilic leucocytosis.

Ross [81] stated that Na⁺ retention is seen in animals with oliguric ARF, but urine Na⁺ loss is higher in polyuric ARF. In renal failure, calcium levels are normally within range or slight lower, whereas phosphorus levels are generally on higher side as compared to CKD.

Cianciolo et al. [11] reported renal insufficiency in an English setter dog caused by ethylene glycol poisoning resulted in azotemia (BUN = 126 mg/dl and creatinine = 12 mg/dl) and marked hyperkalemic changes.

In the cases of renal failure caused by Babesiosis, azotemic dogs had significantly lower amounts of total proteins, albumin, beta and gamma globulins, but significantly higher quantities of alpha-2 globulin. As a result of the liver compensating for protein loss, azotemic dogs have comparatively higher serum cholesterol concentrations. Clinical findings in dogs with AKI includes increased BUN, Cr, hyperphosphatemia, hyper-or hypokalaemia and metabolic acidosis [82].

9.3 Serum renal biomarkers

Biomarkers are considered to be measurable indicators for normal or abnormal metabolic changes [8]. Commonly used biomarkers for renal insufficiency are SDMA, NGAL, Cystatin-C, RBP, Ig-G, UPC, etc., and are considered to be one of the efficient tools for early diagnosis of renal insult.

Creatinine is an indicator of renal function and is inversely correlated with GFR and its rise indicates 75% drop in GFR [83]. Almy et al. [84] reported the mean concentration of Cystatin C in healthy dogs and in dog’s renal failure as 1.08 ± 0.16 mg/l and 4.37 ± 1.79 mg/l, respectively. Fliser et al. [85] reported that asymmetric dimethyl arginine (ADMA) is significantly associated with progression of nondiabetic kidney diseases. Lowering of plasma ADMA concentrations indicates response to therapeutic management of renal disease. Wehner et al. [86] reported high sensitivity and low specificity of Cystatin C as compared to creatinine for the diagnosis of renal failure in dogs. Serum cystatin C is better correlated than serum creatinine with exogenous plasma clearance of creatinine (ECPC), which is an indicator of GFR. Cobrin et al. [9] reported that the cystatin C was superior to creatinine in the assessment of GFR. The urinary biomarkers such as NGAL, KIM-1, IL-18 and NAG were diagnostic of AKI. Biomarkers such as cystatin C, RBP are good for assessing CKD. The biomarker RBP, the micro globulins and NAG A can detect the tubular dysfunction prior to proximal tubular injury. NGAL can detect ischaemic renal injury throughout the tubules and KIM-1 along with IL-18 can detect ischaemic AKI and acute tubular necrosis.

The definitive test to differentiate AKI from CKD is renal histopathology but despite that serum NGAL can differentiate AKI from CKD in dogs with renal azotaemia with 65% sensitivity and 82% specificity [87]. Zhou et al. [88] reported high area under receiver operator characteristics (ROC) curve suggestive of high sensitivity of NGAL and clusterin for detection of gentamicin-induced renal proximal tubular toxicity. NAG is also recognised as potential biomarkers for the early detection of tissue injury in routine toxicity testing due to its high sensitivity.

Grauer [89] studied the assessment of serum NGAL levels in dogs with naturally occurring CKD and found as association between serum NGAL, creatinine and BUN, although NGAL was more related to creatinine. NGAL is reported as good diagnostic and prognostic marker for the diagnosis of stage III and IV CKD. SDMA being more sensitive than creatinine facilitates early diagnosis and treatment of CKD. Subsequent increase in SDMA above normal i.e. more than 14 μg/dL with isosthenuria and normal serum creatinine i.e. <1.4 mg/dl is an early indicator of impaired renal function.

Creatinine is regarded as the major biomarker in RIFLE renal failure staging. To determine AKI grades, a modified IRIS classification is used, which is based on serum creatinine, urine output and the need for renal replacement therapies [90].

Cystatin C permeates through glomerular pores and readily absorbed in proximal tubular cells, with negligible tubular secretion. Thus Cystatin C can be a promising marker for PCT injury [91].

Grauer [31] stated that SDMA is more sensitive than creatinine, aids in the early detection and thus treatment of renal illness. Increase in the levels of serum SDMA (more than 14 mcg/dL) with isosthenuric urine, normal renal echotexture and serum creatinine (more than 1.4 mg/dL) is an indication of kidney injury in dogs.

SDMA remains stable in healthy dogs, but rise with disease progression in sick dogs having renal impairment, associating substantially with an increase in serum creatinine and thus decrease in GFR values [92].

Kielstein et al. [93] indicated that ADMA and SDMA were specific markers of GFR and are good predictors of early renal failure compared to serum creatinine levels, and thus were considered promising biomarkers for the early identification of renal dysfunction in dogs.

NGAL is a potential biomarkers for the early detection of tissue injury associated with various toxicities due to its higher sensitivity in case of early renal injuries [88].