Biomarker . Patient guide
ALT Blood Test
What is ALT
Alanine aminotransferase (ALT) is an enzyme found mainly inside liver cells. When liver cells are inflamed or damaged, ALT leaks into the blood, which makes it the most liver-specific of the routine liver enzymes and a first-line marker of liver-cell injury.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in U/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Adults | approx. 10 to 40 | U/L; upper limit varies between UK labs and by sex |
What it is
ALT catalyses a step in amino-acid metabolism and sits in high concentration inside hepatocytes (liver cells). Because it is far more concentrated in the liver than elsewhere, a raised ALT points quite specifically to the liver, unlike AST which is also found in muscle and heart. It is a core component of a liver function test (LFT).
Why a clinician would order it
ALT is checked to investigate suspected liver problems, to monitor known liver conditions, before and during certain medications (statins, methotrexate), in anyone with risk factors for fatty liver (raised BMI, type 2 diabetes, high alcohol intake), and as part of a general health screen. It is often the first abnormal result that flags non-alcoholic fatty liver disease.
If your level is outside the range
Symptoms of low ALT
What low can indicate. A low ALT is not clinically significant.
Symptoms of high ALT
- Usually none (a raised ALT is found on testing, not felt)
- In advanced liver disease: fatigue, right upper abdominal discomfort, jaundice
What high can indicate. Non-alcoholic fatty liver disease (the commonest cause of a mildly raised ALT in the UK), alcohol-related liver injury, viral hepatitis, and medication effects; very high levels suggest acute hepatitis. ALT higher than AST is typical of fatty liver, whereas AST higher than ALT can suggest alcohol or advanced fibrosis.
Testing tips
No fasting needed. Intense exercise in the days before can transiently raise liver enzymes. A single mildly raised ALT is usually repeated before further investigation, as it can fluctuate.
Where you can get this tested
ALT is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.
Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.
Looking to book a test?
Comprehensive private health screening
Full blood screening at 134 Harley Street, London, reviewed by GMC-registered doctors with a written interpretation.
Symptoms often investigated with ALT
ALT is commonly tested when patients present with the following symptoms. If any of these resonate with you, the linked guides explain what to look for and which test pathway is appropriate.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about ALT
What is a normal ALT range?
Adults: approx. 10 to 40 (U/L; upper limit varies between UK labs and by sex). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low ALT result mean?
A low ALT is not clinically significant.
What does a high ALT result mean?
Non-alcoholic fatty liver disease (the commonest cause of a mildly raised ALT in the UK), alcohol-related liver injury, viral hepatitis, and medication effects; very high levels suggest acute hepatitis. ALT higher than AST is typical of fatty liver, whereas AST higher than ALT can suggest alcohol or advanced fibrosis.
Do I need to fast or prepare for the ALT blood test?
No fasting needed. Intense exercise in the days before can transiently raise liver enzymes. A single mildly raised ALT is usually repeated before further investigation, as it can fluctuate.
Can I order a ALT blood test privately in London?
Yes. WMG Health offers ALT in several standard panels and as part of a custom panel at our 134 Harley Street clinic. Results are released as each marker is reviewed, and the completion date is set by the slowest marker in your panel. We confirm the expected timeframe at booking. Book a standard panel online, or ask for a custom panel via /contact/ or 020 3239 3378.