What does a GGT test measure?
GGT is an enzyme found throughout the body but concentrated in the liver. MedlinePlus explains that when the liver or bile ducts are damaged, GGT leaks into the bloodstream, so a high level may signal liver disease or bile duct damage.
GGT is sensitive but not specific. It tells you the liver is under some kind of stress, and, in general, the higher it is, the more damage there may be. It cannot tell you why. That is why it is almost always read alongside other liver tests rather than on its own.
Why does GGT track drinking so closely?
Alcohol raises it directly. MedlinePlus states that drinking alcohol increases GGT levels, that most people with alcohol use disorder have high GGT, and that the test can be used to screen for or monitor alcohol use. The MedlinePlus encyclopedia also lists alcohol among the substances that can raise GGT.
For men, this makes GGT a useful, nonjudgmental mirror. A man who has four or five drinks most nights may have normal ALT and AST but a raised GGT, and that number can be the first objective sign that drinking is affecting his liver. Seeing it fall on a recheck after cutting back is often more persuasive than any lecture. Our page on heavy drinking and low testosterone covers how the same habit affects hormones.
How does GGT separate liver from bone?
Through its partner enzyme, alkaline phosphatase (ALP). ALP comes from both the liver and the bones, so a high ALP alone could mean either. GGT rises with liver and bile duct problems but not with bone disease, which makes it the tiebreaker.
| ALP | GGT | Most likely source |
|---|---|---|
| High | High | Liver or bile ducts |
| High | Normal or low | Bone |
| Normal | High | Liver stress, such as alcohol, certain medicines or another liver condition |
MedlinePlus spells out the first two rows directly. On the bone side, the MedlinePlus ALP page lists causes such as a healing fracture, Paget disease of bone, an overactive parathyroid and bone tumors, along with a normal range of 40 to 129 IU/L. For an active man with a recent fracture, a high ALP with a normal GGT can simply reflect the bone mending.
What is a normal GGT, and what else raises it?
The MedlinePlus encyclopedia gives a normal adult range of 5 to 40 U/L, and notes that ranges vary among labs. Compare your result with the range on your own report.
Alcohol is only one cause. MedlinePlus lists these among the conditions and substances linked to a higher GGT:
- Liver conditions: hepatitis, cirrhosis, blocked bile flow, liver tumors
- Metabolic and other conditions: diabetes, pancreatitis, heart failure, lung disease
- Medicines: acetaminophen, carbamazepine, phenytoin and phenobarbital
- Smoking, which can also affect the result
Diabetes on that list is worth noting for men carrying weight around the middle, since insulin resistance and fatty liver often travel together. Our page on fatty liver disease in men covers that link, and our ALT and AST liver enzymes page explains the enzymes GGT is usually read with.
How should you prepare for a GGT test?
A few simple steps make the number more meaningful, because GGT responds to food, drink and medicines. MedlinePlus notes that GGT drops after meals, and that medicines, supplements, alcohol and smoking can affect the result. Follow any fasting instruction you are given, avoid alcohol in the days before, and bring a full list of medicines and supplements. Our page on drinking alcohol before a blood test goes into timing.
How Ultimate Male approaches a GGT result
Liver function is part of our Targeted Preventative Health Panel and Comprehensive Health Optimization Panel. GGT is not named on those panel descriptions, so if alcohol, a high ALP or a fatty liver question is on your mind, ask on the free 10-minute call whether the panel you are considering includes GGT or whether to add it.
At your consultation in San Gabriel or Downey, a PA-C or MD reads GGT with your other liver numbers and talks through alcohol honestly and without judgment, including what a recheck would show if you cut back. Our liver and kidney function panel page explains that panel, and every option is on our preventative blood testing page.
