Biomarker . Patient guide
AST Blood Test
What is AST
Aspartate aminotransferase (AST) is an enzyme released when cells are damaged. It is found in the liver but also in muscle and heart, so it is read alongside ALT rather than on its own, and the AST-to-ALT ratio helps point to the likely cause.
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; varies between UK labs |
What it is
AST is involved in amino-acid metabolism and is present in liver, skeletal muscle, cardiac muscle and red blood cells. Because it is less liver-specific than ALT, a raised AST is always interpreted in context, comparing it to ALT and to symptoms.
Why a clinician would order it
AST is part of a liver function test, used to investigate or monitor liver disease and to calculate the AST:ALT ratio. A ratio above 2 raises the possibility of alcohol-related liver disease or advanced fibrosis, whereas a ratio below 1 is more typical of fatty liver.
If your level is outside the range
Symptoms of low AST
What low can indicate. A low AST is not clinically significant.
Symptoms of high AST
- Usually none
- With significant liver injury: fatigue, jaundice, abdominal discomfort
What high can indicate. Liver injury of any cause; because AST is also in muscle, a raised AST with a normal ALT can reflect recent strenuous exercise, a muscle problem, or (rarely) cardiac injury rather than the liver.
Testing tips
No fasting needed. Avoid strenuous exercise for 48 hours before testing, as it can raise AST from muscle. Always read alongside ALT and GGT.
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 AST
What is a normal AST range?
Adults: approx. 10 to 40 (U/L; varies between UK labs). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low AST result mean?
A low AST is not clinically significant.
What does a high AST result mean?
Liver injury of any cause; because AST is also in muscle, a raised AST with a normal ALT can reflect recent strenuous exercise, a muscle problem, or (rarely) cardiac injury rather than the liver.
Do I need to fast or prepare for the AST blood test?
No fasting needed. Avoid strenuous exercise for 48 hours before testing, as it can raise AST from muscle. Always read alongside ALT and GGT.
Can I order a AST blood test privately in London?
Yes. WMG Health offers AST as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.