GGT 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 GGT:
- Optimal 5 – 20 U/L (5 – 20 IU/L); sufficient 5 – 55 U/L (5 – 55 IU/L); out of range below 5 or above 55 U/L.
Evidence grade: Functional / longevity target. A narrower target in common use in functional, integrative, preventive and longevity practice. It is not a universally validated diagnostic range.
At Sera's last range review a change to this band was proposed and held, because the evidence for it was thin, so the band is unchanged. The note below says where it matches published intervals and where it does not.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| U/L | 5 – 20 | 5 – 55 | below 5 or above 55 |
| IU/L | 5 – 20 | 5 – 55 | below 5 or above 55 |
What the evidence says
The acceptable band's upper edge of 55 U/L matches no published interval: Mayo Clinic Laboratories gives 61 for men and 36 for women, MedlinePlus 40 for adults, and NHS sources 38 to 50. A woman between 37 and 55 is therefore above some laboratories' limit while reading Sufficient here. The optimal ceiling of 20 is a functional target; cohort data support lower being better without fixing the number.
Sources
- GGT - Overview: Gamma-Glutamyltransferase (GGT), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult reference interval 8 to 61 U/L in men and 5 to 36 U/L in women. Supports sex-specific sufficient ceilings of 61 and 36 and the lower edge of 5.
- Gamma-glutamyl transferase (GGT) blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal adult range 5 to 40 U/L. Matches Sera's lower edge of 5.
- Association of gamma-glutamyltransferase levels with total mortality, liver-related and cardiovascular outcomes: A prospective cohort study in the UK Biobank — Ho FK, Ferguson LD, Celis-Morales CA, et al. — EClinicalMedicine, 2022 · Peer-reviewed publicationIn 293,667 UK adults, GGT at the common upper limits of normal (48 U/L women, 60 U/L men) carried higher liver-related, cardiovascular and all-cause mortality than 14.5 U/L. Supports a lower optimal target in direction; it does not set 20 as a threshold.
- Assessing liver function and interpreting liver blood tests — NHS Specialist Pharmacy Service, 2024 · Government / public-health guidanceNormal GGT is 0 to 50 IU/L, a single UK figure with no lower limit.
What GGT (Gamma-Glutamyl Transferase) measures
A liver enzyme that is sensitive to problems with the bile ducts.
A sensitive marker of liver health, oxidative stress, and metabolic syndrome.