ALT blood test: what it measures and what your result means

Medically reviewed by Dr Lebeth Jacob · 21 October 2026

Quick answer: ALT (alanine aminotransferase) is an enzyme found mainly in your liver. When liver cells are inflamed or damaged, ALT leaks into the blood, so a raised level is a sign the liver is under strain. In the UK the most common causes are fatty liver and alcohol. A mildly raised ALT is common and often improves with lifestyle changes.

What is ALT?

ALT is an enzyme that helps liver cells turn food into energy. Most of it stays inside the cells. A small amount in the blood is normal; more than that suggests liver cells are being irritated or damaged.

ALT is part of a liver function test, alongside markers such as ALP, GGT, bilirubin and albumin. Looking at them together helps a doctor work out what's going on.

Why is ALT tested?

  • As part of a routine health check or liver function test
  • You're overweight or have type 2 diabetes, which raise the risk of fatty liver
  • You drink alcohol regularly, or want to check your liver after cutting down
  • You take medicines that can affect the liver, such as statins
  • You have symptoms such as tiredness, tummy pain on the right side, or yellowing of the skin or eyes

What does a high ALT result mean?

A raised ALT means liver cells are under strain. Common reasons are:

  • Fatty liver (metabolic dysfunction-associated steatotic liver disease, or MASLD), linked to extra weight and diabetes. This is the most common cause in the UK.
  • Alcohol
  • Some medicines, herbal remedies and supplements
  • Viral hepatitis, such as hepatitis B or C
  • Hard exercise or a muscle injury in the past few days
  • Less common conditions such as coeliac disease, haemochromatosis or autoimmune hepatitis

A mildly raised ALT often settles. A GP will usually repeat the test and may arrange more blood tests or a liver scan if it stays high.

What does a low ALT result mean?

A low ALT is not usually a concern.

What can affect your result?

  • Weight training or other hard exercise in the two or three days before the test can raise ALT
  • Alcohol in the days before can raise it
  • New medicines, herbal remedies or supplements can raise it. Tell the doctor reviewing your result what you take.
  • A recent illness can raise it

When to see a GP

Your results report shows the laboratory's normal range and flags any result outside it. Speak to your GP if:

  • Your ALT is flagged high, especially if it stays high on a repeat test
  • Other liver tests are also raised
  • You have tummy pain on the right side, or feel tired and unwell

Get medical help the same day (GP or NHS 111) if your skin or the whites of your eyes turn yellow, or you have dark urine and pale stools. Go to A&E if you think you may have taken too much paracetamol, even if you feel well.

How we test ALT

You can have ALT tested with a blood sample taken at one of our 250+ partner clinics, or with a finger-prick kit at home. Samples are analysed by a UKAS-accredited laboratory. Results are usually ready in 3–5 working days, with a doctor's comments on every result.

Tests that include ALT

Prices for in-clinic tests include your appointment. Compare every test with ALT in the biomarker explorer

Frequently asked questions

Is my ALT level high?

Your report shows the laboratory's normal range and flags your result if it's outside it. A mildly raised ALT is common, and is often caused by fatty liver, alcohol or recent exercise. A GP will look at how high it is, your other liver tests and whether it stays raised.

When should I worry about my ALT?

Speak to a GP if it's flagged high, especially if it stays high on a repeat test or other liver tests are also abnormal. Get help the same day if you develop jaundice.

How can I lower my ALT?

If fatty liver is the cause, losing weight gradually is the most effective step: losing around 1 in 10 of your body weight can make a big difference. Cutting down on alcohol, being active and managing diabetes help too. Check any supplements or herbal remedies with a pharmacist.

Can exercise raise ALT?

Yes. Hard exercise, especially weight training, can raise ALT for a few days. Avoid it for two or three days before your test.

What is the difference between ALT and AST?

Both are enzymes that rise when liver cells are damaged. ALT is found mainly in the liver. AST is also found in muscle and the heart, so ALT is the more specific liver marker.