D. Request an expedited liver biopsy
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are intracellular enzymes in hepatocytes. Although ALT exists exclusively in the cytoplasm, AST is found in the cytoplasm and mitochondria.1,2 AST is also present in muscles, the kidneys, and the brain; therefore, ALT is more specific for hepatocellular injury. The normal serum AST:ALT ratio is approximately 1. Serum aminotransferase activity is determined by spectrophotometric assays that measure changes in light intensity in a solution, and accurate measurement may be impaired by lipemia, hemolysis, or marked bilirubinemia.
In 2021, the upper reference limits for ALT were redefined as 42 U/L in men and 30 U/L in women.3 For children, the 97th percentile ranges from 30 to 38 U/L in boys and 24 to 32 U/L in girls.4 Metabolic risk factors (including adiposity and hypertension) are associated with higher ALT levels,3 and median ALT and AST levels rise with increasing body mass index classes, likely due to non–alcohol-related fatty liver disease.5 The 2022 Medicare reimbursement rate for serum aminotransferase testing is approximately $5.00 for each enzyme tested. Many liver diseases, such as viral hepatitis or autoimmune hepatitis, present with elevated AST and ALT due to hepatocyte membrane damage and release of these enzymes into the blood (Figure). Aminotransferase levels are typically mildly to moderately elevated (eg, 1.5 to 5 times the upper limit of normal) in non–alcohol-related fatty liver disease, chronic untreated viral hepatitis, acute Budd-Chiari syndrome, acute fatty liver of pregnancy, alcohol-related hepatitis, and cirrhosis. Patients with alcohol-related hepatitis often have serum AST:ALT ratios greater than or equal to 2. Cirrhosis is typically associated with an AST:ALT ratio greater than 1, reflecting reduced hepatocyte production of ALT and impaired clearance of AST by liver sinusoidal cells.