What does the Alanine Aminotransferase test measure?

Why is Alanine Aminotransferase measured?

ALT is the most hepatocyte-specific of the routinely measured aminotransferases and serves as the primary marker of hepatocellular necrosis or membrane injury. Elevation reflects liver damage rather than function, and the magnitude, pattern, and duration guide differential diagnosis: modest chronic rises suggest metabolic dysfunction-associated steatotic liver disease, while marked acute elevations point to viral hepatitis, drug-induced injury, or ischaemic insult. The AST:ALT ratio refines interpretation — a ratio less than one is typical of steatotic disease, whereas a ratio greater than two raises suspicion for alcohol-related hepatitis.

Reference ranges

Standard reference

Approximately 10–40 U/L in men and 7–35 U/L in women; assay- and population-dependent.

Functional medicine optimal

Functional and preventive-medicine practitioners often advocate lower healthy thresholds — around 25–30 U/L in men and 19–25 U/L in women — derived from healthy lean populations, though these cutoffs are not universally adopted in standard laboratory reporting.

Units

U/L, µkat/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.