GPT (ALT)
Liver-specific enzyme and primary indicator of liver damage
Also known as
Definition
GPT (alanine aminotransferase, ALT) is the most liver-specific of the classic transaminases and the most sensitive marker for hepatocellular damage. Elevated values occur with fatty liver disease (NAFLD), drug-induced hepatotoxicity, viral hepatitis, and intense physical exertion. GPT is always interpreted in conjunction with GOT.
| Parameter | Value |
|---|---|
| Unit | U/l (IU/l) |
| Reference Range | Women: < 35 U/l | Men: < 50 U/l |
| Optimal Range (lab2go) | < 20 U/l |
↓ What a low value means
Very low GPT values have no independent clinical disease value. With severe malnutrition or vitamin B6 deficiency, GPT may appear reduced. Clinically relevant hypertransaminasemia is rare and occurs primarily in terminal liver failure (enzyme deficiency from parenchymal loss).
↑ What a high value means
Elevated GPT is the most sensitive indicator of hepatocellular damage: fatty liver (NAFLD/NASH), viral hepatitis B and C, alcoholic hepatitis, drug-induced hepatotoxicity (acetaminophen, NSAIDs, rarely statins), autoimmune hepatitis, celiac disease. GPT > 3× normal = significant liver damage; > 10× = acute hepatitis or drug toxicity. With isolated GPT elevation without cause: rule out celiac antibodies (anti-tTG IgA).
✓ How to optimize this marker
Avoid alcohol. Weight loss: 5–10% body weight reduction frequently normalizes GPT in NAFLD. Review hepatotoxic medications and supplements (herbs, bodybuilding supplements). Sugar-reduced diet lowers liver fat. Regular exercise (150 min/week moderate intensity) reduces hepatic fat independently of weight.
When to test
As part of the liver panel with GOT and GGT. No fasting required; avoid intense physical exercise 48 hours before (less muscle involvement than GOT, but still possible). Repeat elevated values after 4–6 weeks without confounders.
Frequently asked questions
What is the difference between GPT and GOT? +
GPT is more liver-specific than GOT. GOT is also found in cardiac, muscle, and kidney cells. Isolated GPT elevation almost always indicates a liver problem; isolated GOT elevation can also originate from muscle.
Can supplements elevate GPT? +
Yes. Herbal preparations (e.g., kava, high-dose green tea extract, high-dose valerian), certain bodybuilding supplements, and high-dose niacin can raise GPT. Inform your physician about all supplements being taken.
What GPT level warrants a liver biopsy? +
Persistently elevated GPT (> 6 months) of unclear cause after ruling out common differential diagnoses, or when fibrosis/cirrhosis is suspected, may warrant biopsy or FibroScan (elastography). The final decision rests with a gastroenterologist/hepatologist.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.