Biomarker Glossary

ALT

ALT (alanine aminotransferase) is a liver enzyme. A small amount circulates in the blood normally, but levels rise when liver cells are damaged. ALT is the most specific blood marker of liver injury and a standard test in any UK liver health, metabolic or general health screen.

Also known as: Alanine Aminotransferase, SGPT, Alanine Transaminase

ALT is most informative when read alongside related markers like AST and GGT. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.

What is ALT?

ALT is mostly found inside liver cells. When a liver cell is damaged or destroyed (by fat, alcohol, viruses, drugs or autoimmune disease), it releases ALT into the bloodstream.

Because ALT is highly concentrated in the liver and only in small amounts elsewhere, it is the most liver specific of the common liver enzymes. AST, GGT and alkaline phosphatase are usually tested alongside to characterise the type of liver problem.

Mildly raised ALT is very common in the UK, most often from non alcoholic fatty liver disease (now called metabolic associated fatty liver disease, MAFLD). Significantly raised ALT (over 200 IU/L) suggests acute hepatitis, drug toxicity or autoimmune disease.

Why test ALT?

  • To investigate suspected liver problems, fatigue, weight gain or alcohol related concerns.
  • To screen for fatty liver, which is now the most common liver disease in the UK.
  • If you take medications that can affect the liver (statins, paracetamol, methotrexate).
  • To monitor known liver conditions (hepatitis, fatty liver, alcohol related liver disease).
  • As part of any general health or metabolic syndrome screen.
To investigate suspected liver problems, fatigue, weight gain or alcohol related concerns.

ALT normal range (UK)

Result What it means
Men: 10 to 45 IU/L Normal (standard NHS lab range)
Women: 10 to 35 IU/L Normal (standard NHS lab range)
Mildly raised (up to 2 to 3 times the upper limit) Most often fatty liver, alcohol, mild medication effect
Significantly raised (above 200 IU/L) Often acute hepatitis, drug toxicity, autoimmune liver disease

Ranges vary slightly between labs. Some researchers argue the upper normal range should be lower (around 30 IU/L for men, 20 IU/L for women) for early detection of fatty liver.

About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.

What causes high ALT?

  • Non alcoholic fatty liver disease (NAFLD or MAFLD), the most common cause in the UK
  • Alcohol related liver disease
  • Viral hepatitis (hepatitis B, C)
  • Medication induced liver injury (paracetamol overdose, statins, some antibiotics)
  • Autoimmune hepatitis
  • Coeliac disease
  • Haemochromatosis (iron overload)
  • Wilson's disease (copper overload)
  • Strenuous exercise (transient rise)
  • Muscle injury (small amounts of ALT are also in muscle)

What causes low ALT?

  • Low ALT is generally not clinically significant.
  • May indicate vitamin B6 deficiency in rare cases.
  • Older age is associated with lower ALT.

Symptoms of high ALT

  • Often no symptoms in early liver disease (the liver is a quiet organ).
  • Fatigue is common.
  • Discomfort or fullness in the upper right abdomen.
  • Yellowing of skin or eyes (jaundice) in more advanced disease.
  • Itching, dark urine, pale stools in significant liver disease.
  • Bruising or bleeding easily in late stage disease.

Symptoms of low ALT

  • No specific symptoms.

How is ALT tested?

ALT is measured from a small blood sample. No fasting is required.

Avoid strenuous exercise for 24 hours before the test, as muscle damage can transiently raise ALT.

Tested alongside AST, GGT and alkaline phosphatase for a full liver function picture.

Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.

How to support healthy ALT levels

  • Lose weight if needed. Even 5 to 10 percent weight loss significantly reduces ALT in fatty liver disease.
  • Reduce or eliminate alcohol. Many people see ALT halve within weeks of stopping drinking.
  • Cut back on sugar, fructose and refined carbohydrates. These drive fatty liver more than dietary fat does.
  • Increase physical activity. Both aerobic exercise and strength training lower liver fat independently of weight loss.
  • Limit unnecessary medications and supplements. Always tell your healthcare team what you are taking.
  • Coffee (2 to 3 cups per day) is protective against liver disease in observational studies.

These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.

Chxhealth panels that test ALT

12 Chxhealth biomarker panels include ALT. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.

ALT FAQs

What is a normal ALT level?

10 to 45 IU/L in men and 10 to 35 IU/L in women is the standard NHS range. Some researchers consider levels above 30 in men and 20 in women as early indicators of fatty liver.

What is the most common cause of raised ALT in the UK?

Non alcoholic fatty liver disease (NAFLD or MAFLD), now affecting around 1 in 3 UK adults. It is closely tied to weight, insulin resistance and diet.

Can exercise raise ALT?

Yes. Strenuous exercise (heavy weights, marathon training) can transiently raise ALT for several days. Avoid intense exercise for 24 to 48 hours before liver testing.

Can fatty liver be reversed?

Yes, particularly in early stages. Weight loss, dietary changes and exercise reliably lower liver fat and ALT in most people. Even cirrhosis can be stabilised or slowed with the right interventions.

What is the difference between ALT and AST?

Both are liver enzymes. ALT is more specific to the liver, while AST is also found in heart and muscle. The AST to ALT ratio helps distinguish causes: above 2 suggests alcohol related liver disease, while below 1 typically indicates fatty liver.

Often tested with ALT

The biomarkers below are commonly investigated alongside ALT because they reveal connected aspects of the same physiological picture:

  • AST: AST-to-ALT ratio helps distinguish alcoholic from non-alcoholic patterns.
  • GGT: GGT is more sensitive to alcohol and biliary issues.
  • Triglycerides: Fatty liver typically raises both.
  • Cholesterol: Lipid markers complete the metabolic liver picture.

Choose the right test for your goal

If you are reading about ALT because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:

Sources and further reading

This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:

About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.

Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.