Influence of Local Reference Populations on Upper Limits of Normal for Serum Alanine Aminotransferase Levels

Abstract

Chronic liver disease can progress to cirrhosis if not detected early and appropriate interventions taken when possible. Serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase are commonly measured during routine health care examinations to detect such unsuspected liver disease. Care providers often use the reporting laboratory's ALT upper reference limit (upper limit of normal [ULN]) or a multiple thereof (eg, 1.5 × ULN) to trigger further evaluation. Such evaluation can be expensive and invasive, yet ignoring aminotransferase elevations can allow life-threatening liver disease to progress if not recognized and treated appropriately. Therefore, how clinical laboratories define their own ALT ULN values is critically important in determining the risk-benefit ratio of further evaluation.