Changing Perspectives on Liver Testing
To provide high-quality, cost-effective healthcare, a rational approach to the appropriate evaluation of serum liver chemistries is essential for all healthcare professionals. As is the case for all medical tests, liver chemistries must be interpreted in the context of the patient's risk factors for disease, symptoms, and history and physical examination findings.[1]
This overview provides an updated perspective on this issue in the context of recently announced guidance.[2]
What Current Panels Provide
Comprehensive metabolic profile testing (panels) is widely used to screen individuals who present for routine evaluation, as well as those referred for elevated liver enzyme values. The standard comprehensive, most commonly ordered panel includes measurement of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, and bilirubin.
These liver chemistry tests are indirect markers of hepatobiliary disease or liver injury; they are not "liver function tests." True tests of liver function include prothrombin time and others that are not commonly performed, such as measurement of hepatic substrates that are cleared by hepatic uptake or metabolism.
The pattern of findings on liver chemistry tests may provide clues to the nature of the injury. Hepatocellular disease is typically defined as a disproportionate elevation of the AST and ALT levels compared with alkaline phosphatase levels, whereas cholestatic disease is signaled by a disproportionate elevation of the alkaline phosphatase level compared with AST and ALT levels.
