The umbilical cord blood (UCB) can be used for early detection of neonatal diseases. The UCB can be used for early detection of neonatal diseases. Establishing reference intervals is essential for appropriate interpretation of results of laboratory tests using UCB and for correct medical decisions of pediatricians and neonatologists. The use of proper reference intervals provides reliable information to pediatricians and neonatologists; thus, they could make correct medical decisions for neonates. This chapter discussed reference intervals of platelets, lymphocytes, and cardiac biomarkers in UCB according to the Clinical Laboratory Standards Institute guidelines. Except iatrogenic anemia, thrombocytopenia is the most common hematologic abnormality in neonates. Immature platelet fraction is a novel parameter to estimate megakaryopoiesis and can be useful to understand the mechanism of thrombocytopenia, platelet destruction or bone marrow failure, in neonates. Lymphocyte counts, T cell and B cell, can reflect status of immune system in fetus and neonates. Especially Tregs in UCB may contribute to maintain the immune homeostasis in the feto‐maternal relationship, and the presence of Tregs would be essential to prevent immune dysregulation in fetus and neonates. Congenital heart disease or defect is the most common birth defect in newborns. Cardiac biomarkers are essential to evaluate heart function and to give information of myocardial injury, necrosis, or myocardial stretch. There are no current guidelines for their routine use in children.