Liver and pancreas
Gamma-GT
An enzyme from the liver and bile ducts that rises when the liver is under strain, mainly from alcohol, medicines or a bile duct problem.
Everything about this testWhat it measures
Gamma-GT (gamma-glutamyltransferase, GGT) is an enzyme found mainly in the cells of the liver and the small bile ducts. It enters the blood when those cells are irritated or damaged. This happens with alcohol use, with many medicines, with fatty liver and when the outflow of bile is blocked. Gamma-GT is often assessed together with alkaline phosphatase: if alkaline phosphatase is raised, a raised gamma-GT indicates that the cause lies in the liver or bile ducts and not in the bone.
- Strain on the liver from alcohol (gamma-GT is the most sensitive routine test for this, but not specific)
- Blocked bile outflow (cholestasis), for example due to gallstones or a narrowing of the bile duct
- Liver damage from medicines or fatty liver
- Distinguishing between liver and bone when alkaline phosphatase is raised
High
A raised gamma-GT is common and is not a diagnosis on its own. The most common causes are regular alcohol use (even a few glasses in the days before the blood draw), fatty liver with overweight or diabetes, and medicines such as antiepileptics, some antidepressants, antibiotics and statins. After stopping alcohol, it often takes a few weeks to a month before the value is normal again. A strongly raised gamma-GT together with a raised alkaline phosphatase and bilirubin fits obstructed bile outflow; symptoms are then pain in the upper right abdomen, jaundice, itching, dark urine and pale stool. Smoking and a higher weight also give a higher gamma-GT on average.
Low
A low gamma-GT has no significance. The value is lower on average in women than in men and falls with use of the contraceptive pill.
If your result is abnormal
The GP assesses gamma-GT together with ALT, alkaline phosphatase and bilirubin, and asks about alcohol and medicines. With a raised value without symptoms, a repeat measurement usually follows after a few weeks without alcohol; if the value stays raised, testing for fatty liver follows and, if needed, an ultrasound of the liver and bile ducts.
Reliability
Gamma-GT is sensitive but not very specific: it rises with many different causes and says nothing about the severity of liver damage. As a test for excessive alcohol use, gamma-GT has limited value: according to the Dutch GP guideline (NHG) on problematic alcohol use, some people who drink too much have a normal gamma-GT, and a raised value often has another cause. For the question of how much someone drinks, a conversation or questionnaire is more reliable than a blood test; CDT is more specific for alcohol but less sensitive.
Limitations
- Alcohol in the week before the blood draw raises the value; even a single evening of heavy drinking can raise gamma-GT for a day.
- Many medicines raise gamma-GT without liver damage, including antiepileptics (carbamazepine, phenytoin), some antidepressants and statins.
- Overweight, diabetes and smoking give higher values on average; men have higher values than women.
- Reference values differ per laboratory.
How common is this
Excessive alcohol use (more than 21 glasses per week for men or 14 for women) occurs in about 5 to 6 in 100 adults in the Netherlands, about twice as often in men as in women. In a large proportion of them, gamma-GT is raised. A raised gamma-GT due to fatty liver or medicines is even more common.
Who is this useful for
Useful with a raised alkaline phosphatase to distinguish between liver and bone, when a bile duct problem is suspected, when monitoring liver damage from medicines, and when you want to see for yourself whether alcohol is putting strain on your liver, for example when cutting down or stopping. In healthy adults without risk factors, routine measurement is not needed.
Downsides and risks
- A raised gamma-GT is quickly linked to alcohol, while fatty liver and medicines are just as often the cause; this can unfairly label someone.
- A normal gamma-GT does not rule out excessive alcohol use.
Sources
- NHG-Standaard Virushepatitis en andere leveraandoeningen (M22)
- NHG-Standaard Problematisch alcoholgebruik (M10)
- NVKC, allesovertesten.nl: GGT
- Thuisarts.nl: Ik vraag me af of ik te veel alcohol drink
- VZinfo (RIVM): Alcoholgebruik volwassenen
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results