ALT
A liver enzyme that rises when liver cells are irritated — most often from fatty liver.
What it means
An enzyme found inside liver cells. When those cells are irritated or damaged, it leaks into the blood and the level rises.
Mildly raised ALT is one of the commonest abnormal results on any blood panel, and in the UK the commonest cause by a distance is fatty liver — fat accumulating in the liver, usually alongside excess weight, alcohol, or insulin resistance.
"Liver function tests" is a slightly misleading name. ALT measures cell irritation rather than how well the liver is working. Albumin and clotting are the tests that actually reflect function.
In practice
On any LFT panel, health screen, or monitoring bloods for medicines such as statins or methotrexate.
Usually reported with AST, ALP, GGT, bilirubin and albumin, and the pattern between them matters more than any single figure.
Why it matters
Do not panic at a mildly raised figure, and do not ignore it either. Fatty liver is common, silent, and genuinely reversible — around 7 to 10% weight loss substantially improves it.
Be honest about alcohol. The number is more useful to whoever is reading it than a tidy answer is.
Ask for a repeat and, if it stays up, for the standard liver screen — viral hepatitis, autoimmune and iron studies, and an ultrasound. Persistent abnormality deserves a cause, not another repeat in six months indefinitely.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026