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ALT

An enzyme concentrated in liver cells. When liver cells are injured, ALT leaks into the blood, so the level is a marker of hepatocellular damage rather than of liver function. It is usually reported with AST, ALP, GGT and bilirubin, and the pattern across those five says more than any one of them.

General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.

Usual adult reference range

The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.

Source: Commonly quoted adult upper reference limits; the exact figure is method-dependent and differs between laboratories, and lower thresholds have been proposed. · checked 2026-09-02

What a high result generally indicates

A raised ALT means liver cells are being damaged. The commonest reasons in Europe are fatty liver disease, alcohol, medicines and supplements, and viral hepatitis. Mild elevations are very common and are usually rechecked before anything else happens. A large rise is investigated promptly.

What a low result generally indicates

A low ALT is not clinically meaningful on a routine report.

These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.

What affects this result

• Alcohol in the days before the test.
• Body weight — fatty liver is the most common cause of a mild rise.
• Medicines and supplements, including paracetamol at high doses and some herbal products.
• Vigorous exercise or muscle injury raises AST more than ALT, but can move both.
• Viral hepatitis, past or present.
• Coeliac disease and thyroid disease can both raise it.

Before the test

No fasting needed for ALT itself; it is often bundled with tests that do require fasting.

Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.

The one thing to take from this page

The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.

Frequently asked questions

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