Laboratory assessment of liver function and injury in children

The liver is a multifunctional organ that is involved in a number of critical excretory, synthetic, and metabolic functions. Biochemical assessment of these functions in children involves a number of tests performed in clinical laboratories. Many of the most commonly utilized serum chemistry tests, such as the aminotransferase and alkaline phosphatase (AP) levels, are often referred to as liver function tests, which is a misnomer as these do not actually measure or indicate liver function. Rather, these tests should be referred to as liver enzyme tests, with the term liver function tests reserved for true measures of hepatocyte synthetic function such as serum albumin levels and the prothrombin time (PT) or international normalized ratio. Any single biochemical test provides limited information that must be placed in the context of the entire clinical and historical picture. Currently available laboratory evaluative tests of the liver are used to: (1) screen for and document liver injury; (2) identify the type or pattern of liver disorder and the site of injury; (3) make a prognosis and follow-up children with chronic liver disease; and (4) serially monitor the course of liver disease, evaluate the response to treatment, and adjust a treatment regimen, when appropriate. The widespread availability and frequent use of serum chemistry tests in children have resulted in an increase in the number of both normal and abnormal liver chemistry test values that must be evaluated by physicians. However, some limitations of liver biochemical tests must be recognized. First, screening laboratory tests may lack sensitivity. That is, if a liver chemistry test is normal, it does not ensure that the patient is free of liver disease. Children with chronic liver disease can have normal serum aminotransferase levels. Second, these tests are not specific for liver dysfunction. For example, serum aminotransferases may be elevated in patients with a non-hepatic disorder such as a musculoskeletal condition or cardiomyopathy. Finally, liver chemistry tests rarely provide a specific diagnosis; rather, they suggest a general category of liver disorder. For example, abnormal liver biochemical tests do not distinguish viral hepatitis from autoimmune hepatitis, or delineate intrahepatic from extrahepatic etiologies of cholestasis.