ALT is an enzyme that lives mainly inside liver cells. While the cells are intact, little of it reaches the blood. As soon as liver cells are damaged, ALT leaks out — and its blood level rises.
That is exactly why ALT is one of the most sensitive and specific markers of liver status. It is almost always looked at together with AST.
Reference ranges
Approximate reference for adults (venous blood):
| Men | up to 41 U/L |
| Women | up to 33 U/L |
| Important | reference ranges depend on the lab and method |
What an elevated level means
An elevated ALT means liver cells are being damaged. The most common causes are not viruses at all:
Metabolic: fatty liver disease (NAFLD) — the number-one cause worldwide; excess weight, insulin resistance.
Toxic: alcohol, medications (including paracetamol, statins, antibiotics), supplements.
Viral and other: hepatitis B and C, autoimmune liver diseases.
A sharp rise (10× or more) is a reason to seek care urgently; a moderate one calls for a calm search for the cause and a repeat test.
What a low level means
A low ALT usually has no clinical significance and is not specifically corrected. Very low values are sometimes linked to a deficiency of vitamin B6 (the enzyme's cofactor) or to general wasting.
How the test is done
Venous blood, fasting (8–12 hours), in the morning.
For 2–3 days before the test avoid alcohol and intense strength training — both can inflate the result. Discuss any medications and supplements with your doctor.
What affects the value
- Alcohol — even a single episode the day before raises ALT.
- Excess weight and insulin resistance — lead to fatty liver and a rise in ALT.
- Medications and supplements — many are hepatotoxic.
- Physical activity — heavy workouts temporarily raise the level.
- Sex — the normal range is higher in men than in women.
Calculate using this marker
Calculators where ALT (alanine aminotransferase) is used directly:
Frequently asked questions
ALT is elevated — is it dangerous?
A moderate rise on its own (1.5–2×) is most often linked to fatty liver or alcohol and is not an emergency. But it cannot be ignored — the cause must be found and addressed. A sharp rise (10× or more) requires urgent medical attention.
How does ALT differ from AST?
ALT is more specific to the liver — almost all of it is in liver cells. AST is also present in the heart and muscles. That is why they are always assessed together, and their ratio (the De Ritis coefficient) helps pin down the cause.
How do I lower ALT quickly?
If the cause is fatty liver, weight loss, giving up alcohol, physical activity and cutting sugar in the diet help. ALT usually falls over a few weeks to months. There are no special "liver pills" with proven benefit here — lifestyle is what works.