ALT 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 ALT:
- Optimal 7 – 20 U/L (7 – 20 IU/L); sufficient 7 – 45 U/L (7 – 45 IU/L); out of range below 7 or above 45 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 | 7 – 20 | 7 – 45 | below 7 or above 45 |
| IU/L | 7 – 20 | 7 – 45 | below 7 or above 45 |
What the evidence says
The acceptable band of 7 to 45 U/L is a laboratory reference interval: it is Mayo Clinic Laboratories' interval for women, and Mayo's limit for men is higher at 55. Other reputable sources stop lower (MedlinePlus 36, NHS 40), so read a result near the top against the range on the report. The optimal band ending at 20 U/L is a stricter functional target with no published threshold behind it: the American College of Gastroenterology puts the healthy-normal limit at 33 U/L in men and 25 in women, and says levels above that should be assessed. A low ALT has no established clinical meaning.
Sources
- ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries — Kwo PY, Cohen SM, Lim JK — The American Journal of Gastroenterology, 2017 · Clinical guidelineCurrent edition in force. A true healthy normal ALT is up to 29 to 33 IU/L in men and 19 to 25 IU/L in women; higher levels should be assessed. Supports the proposed optimal ceilings of 33 (men) and 25 (women).
- ALT - Overview: Alanine Aminotransferase (ALT) (GPT), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult reference interval 7 to 55 U/L in men and 7 to 45 U/L in women. Matches Sera's lower edge of 7 and, for women, the sufficient upper edge of 45.
- Alanine transaminase (ALT) blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal range 4 to 36 U/L. A tighter upper limit than Sera's 45 and a lower floor than Sera's 7.
- Assessing liver function and interpreting liver blood tests — NHS Specialist Pharmacy Service, 2024 · Government / public-health guidanceNormal ALT and AST are 0 to 40 IU/L. UK figure, close to Sera's ALT upper edge of 45 and with no lower limit.
What ALT (Alanine Aminotransferase) measures
An enzyme that lives mainly inside liver cells.
Raised ALT is a sign of liver stress or damage. Worth watching when taking medicines.