AST optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for AST:
- Optimal 8 – 20 U/L (8 – 20 IU/L); sufficient 8 – 40 U/L (8 – 40 IU/L); out of range below 8 or above 40 U/L.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| U/L | 8 – 20 | 8 – 40 | below 8 or above 40 |
| IU/L | 8 – 20 | 8 – 40 | below 8 or above 40 |
What the evidence says
The acceptable band is a laboratory reference interval: the NHS gives a normal AST of up to 40 IU/L, and Mayo Clinic Laboratories and MedlinePlus put the lower limit at 8. Mayo's upper limits are slightly higher (48 in men, 43 in women), so read a result just above 40 against the range on the report. The optimal ceiling of 20 U/L is a functional target; no guideline or cohort source was found for it. AST also comes from muscle, so hard exercise or muscle injury can raise it without liver disease. A low AST has no established clinical meaning.
Sources
- Assessing liver function and interpreting liver blood tests — NHS Specialist Pharmacy Service, 2024 · Government / public-health guidanceNormal AST is 0 to 40 IU/L. Matches Sera's sufficient upper edge of 40; gives no lower limit.
- AST - Overview: Aspartate Aminotransferase (AST) (GOT), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult reference interval 8 to 48 U/L in men and 8 to 43 U/L in women. Supports a lower edge of 8, not 10; upper limits are a little above Sera's 40.
- Aspartate aminotransferase (AST) blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal range 8 to 33 U/L. Supports a lower edge of 8.
What AST (Aspartate Aminotransferase) measures
An enzyme found in the liver and also in muscle.
Raised AST can point to liver problems, muscle damage, or metabolic issues.