ALT (SGPT) — Normal Range & Interpretation

Clinical Context

ALT (alanine aminotransferase), formerly called SGPT, is an enzyme concentrated in hepatocytes that catalyzes amino acid metabolism. When liver cells are injured, ALT leaks into the bloodstream, making it the most specific serum marker for hepatocellular damage. Unlike AST, which appears in heart, muscle, and kidney tissue, ALT elevation points directly to the liver, giving it superior specificity in differential diagnosis.

Elevations occur with viral hepatitis, nonalcoholic fatty liver disease, medication-induced injury (statins, acetaminophen, isoniazid, methotrexate), alcohol use, autoimmune hepatitis, and ischemic liver injury. Marked elevations above 1000 U/L suggest acute viral hepatitis, toxin exposure, or ischemia. An AST:ALT ratio greater than 2:1 suggests alcoholic liver disease, while a ratio less than 1 suggests nonalcoholic fatty liver or viral etiology. Low ALT carries minimal clinical significance.

FNPs see ALT on the boards most often in scenarios requiring distinction from AST in terms of tissue specificity, interpret the AST:ALT ratio to identify alcoholic versus nonalcoholic liver disease, and recognize hepatotoxic medications requiring ALT monitoring. Expect questions linking statin therapy initiation to baseline ALT assessment, acetaminophen overdose patterns, and chronic hepatitis screening. Candidates must identify ALT as the more liver-specific enzyme and recognize patterns pointing toward specific hepatic pathologies.

Related Labs

• AST (SGOT) — U/L
• ALP — U/L
• Total Bilirubin — mg/dL
• Direct Bilirubin — mg/dL
• Albumin — g/dL

Sources

• MedlinePlus
• ARUP Consult