What does the Alanine Aminotransferase (ALT, SGPT) test measure?

Why is Alanine Aminotransferase (ALT, SGPT) measured?

ALT is the primary hepatocellular injury marker in the CMP — the most sensitive indicator of active hepatocyte damage from any cause: viral hepatitis (acute or chronic), non-alcoholic fatty liver disease (NAFLD), alcoholic hepatitis, autoimmune hepatitis, drug-induced liver injury (DILI), ischaemic hepatitis, and metabolic causes. The magnitude of ALT elevation provides prognostic information: mild elevation (1–3× ULN) is non-specific and common in NAFLD and medication effect; moderate elevation (3–10× ULN) warrants hepatic investigation; severe elevation (>10–20× ULN) suggests acute hepatocellular necrosis from viral hepatitis, ischaemia, or toxin. The ALT:AST ratio provides aetiological clues — ratio >2:1 favours NAFLD or viral hepatitis; ratio >3:1 with high absolute values suggests alcoholic liver disease.

Reference ranges

Standard reference

Male: 7–56 U/L; Female: 7–35 U/L # REVIEWER FLAG: Confirm Quest Diagnostics sex-specific reference ranges for ALT — there is significant debate about the appropriate upper limit for females, with Prati et al. (NEJM 2002) proposing sex-specific limits of 30 U/L for males and 19 U/L for females as more sensitive for early liver disease; confirm whether Quest applies sex-specific ALT ranges and their specific upper limits.

Functional medicine optimal

<25 U/L for females; <30 U/L for males (functional medicine and emerging hepatology optimal, based on Prati et al. sex-specific upper limits associated with absence of histological liver disease in population-based studies). # REVIEWER FLAG: The Prati et al. lower sex-specific ALT thresholds are not yet universally adopted in mainstream laboratory reference ranges — reviewer to confirm appropriate framing.

Units

U/L, IU/L

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