Liver function tests: what each marker reflects
Where ALT, AST, ALP, GGT, bilirubin, albumin and INR come from, their half-lives and non-hepatic sources, how to classify a pattern with the R ratio, what very high transaminases and an AST to ALT ratio mean, and which markers actually measure liver function, with worked examples.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Most "liver function tests" measure injury, not function. ALT and AST leak from damaged hepatocytes; ALP and GGT rise with cholestasis. Only bilirubin, albumin and INR reflect what the liver can do.
- Sort a pattern first: hepatocellular, cholestatic or mixed, using the R ratio. Then judge magnitude: borderline, moderate, or over 1,000 U/L.
- Every marker has non-hepatic sources and a half-life. Those two facts explain most exam traps.
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Sources
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol 2017;112(1):18-35American College of Gastroenterology, 2017
- Newsome PN et al. Guidelines on the management of abnormal liver blood tests. Gut 2018;67(1):6-19British Society of Gastroenterology, 2018
- Sherlock's Diseases of the Liver and Biliary System (13th ed.)Wiley-Blackwell (Dooley, Lok, Garcia-Tsao, Pinzani, 2018), 2018
- Chalasani NP et al. ACG Clinical Guideline: Diagnosis and Management of Idiosyncratic Drug-Induced Liver Injury. Am J Gastroenterol 2021;116(5):878-98American College of Gastroenterology, 2021
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Deploy to Cloudflare on push to main