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 |
Agree on your personal target range with your doctor.
↓ What a low value means
Very low GPT values have no independent clinical significance. With severe malnutrition or vitamin B6 deficiency, GPT may appear reduced. Clinically relevant hypotransaminasemia 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. The degree of elevation does not directly indicate the extent of the damage (AASLD); very high values occur, for example, in acute viral hepatitis or drug- or toxin-induced liver injury, while mild elevations are common in fatty liver. With an isolated GPT elevation without an obvious cause, celiac disease can also be behind it; it can be checked via antibodies (anti-tTG IgA).
✓ What can influence this value
GPT (ALT) is influenced by alcohol consumption, fatty liver diseases (NAFLD) and body weight, viral liver diseases, and liver-toxic medications and preparations (for example certain herbal products or bodybuilding supplements). A sugar-rich diet can increase liver fat content, while regular physical activity can reduce it independently of weight. Intense exertion can raise the value temporarily. The assessment is made by the treating doctor.
When to test
As part of the liver panel with GOT and GGT. Fasting is not required. Intense physical exercise before the blood draw can raise the value, though less than GOT. Whether and when it is measured again is decided by your doctor.
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. For the interpretation it therefore matters which supplements you take.
When is a liver biopsy considered? +
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.
GPT (ALT)
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.