Gamma-Glutamyl Transferase (GGT) Unit Converter
Gamma-Glutamyl Transferase (GGT) Unit Converter
Convert gamma-glutamyl transferase between U/L, IU/L, µkat/L and nkat/L, with sex-specific ranges and what an isolated rise means.
Gamma-Glutamyl Transferase (GGT) converter
Activity unitsGGT 64 U/L
Formula and conversion factor
U/L = µkat/L × 60
- U
- 1 unit = 1 µmol of substrate converted per minute
- kat
- 1 katal = 1 mol of substrate converted per second
- ÷ 60
- the only difference between the two is per-minute versus per-second
- IU/L
- numerically identical to U/L
Worked example
GGT 64 U/L
64 ÷ 60 = 1.067 µkat/L
= 1067 nkat/L = 64 IU/L
Common causes of a raised GGT
| Category | Examples |
|---|---|
| Alcohol | Regular or recent heavy intake |
| Enzyme-inducing drugs | Phenytoin, carbamazepine, barbiturates, rifampicin |
| Hepatobiliary | Fatty liver, biliary obstruction, cholestasis |
| Metabolic | Obesity, type 2 diabetes, hyperthyroidism |
| Other | Heart failure, COPD |
What GGT measures
Gamma-glutamyl transferase sits on the membrane of biliary epithelial cells and hepatocytes. Its chief clinical use is not as a liver test in its own right but as a tissue-of-origin marker: because GGT is absent from bone, it tells you whether a raised alkaline phosphatase is hepatobiliary or skeletal, which is a question the ALP alone cannot answer.
As an independent test it is sensitive and almost entirely non-specific. GGT is induced by alcohol, by phenytoin, carbamazepine, barbiturates and many other drugs, and is raised in fatty liver disease, biliary obstruction, heart failure, chronic obstructive pulmonary disease, diabetes, obesity and hyperthyroidism. An isolated elevation in an otherwise well patient with normal transaminases and a normal ALP is common and, in the absence of other findings, usually reflects alcohol, medication or metabolic fatty liver rather than a discrete lesion.
It is a poor test for detecting alcohol use in isolation, since it lacks both sensitivity and specificity, though a fall over several weeks of abstinence can be useful as a marker of change within an individual. Epidemiologically, a raised GGT is associated with cardiovascular and all-cause mortality independently of alcohol intake, which is interesting but does not translate into a screening role.
Frequently asked questions
How do I convert GGT from U/L to µkat/L?
Divide by 60. A GGT of 64 U/L is 1.067 µkat/L.
What does an isolated raised GGT mean?
With normal transaminases and a normal ALP it is usually alcohol, an enzyme-inducing medication or metabolic fatty liver. In a well patient with no other abnormality it rarely warrants imaging on its own.
Is GGT a test for alcohol use?
Not a reliable one. It lacks both sensitivity and specificity, since many drugs and conditions raise it. A fall during abstinence can be useful within an individual as a marker of change.
Why is GGT measured alongside ALP?
GGT is present in biliary epithelium but not in bone, so it identifies whether a raised ALP is hepatobiliary or skeletal in origin.
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References
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35.
- IFCC reference procedure for gamma-glutamyltransferase at 37°C.