GGT blood test: normal range and what high GGT means

Quick answer: on a GGT blood test, MedlinePlus gives a normal adult range of 5 to 40 U/L (0.08 to 0.67 microkat/L). Cleveland Clinic says the normal range is often below 50 U/L but varies by sex, age and lab. A high GGT usually points to the liver or bile ducts, and alcohol is one of the most common reasons. On its own it does not say which condition you have; it is read with ALT, AST and ALP.

GGT with the full liver panelGGT is on SiPhox GLP Optimization and Ultimate 360, with ALT, AST, ALP and bilirubin.

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GGT normal range

Ranges can differ by sex and age, so many labs print separate ranges. Always check the range on your own report, and note whether you drank alcohol in the day before the test.

What is GGT?

Gamma-glutamyl transferase is an enzyme found mostly in the liver, with smaller amounts in the kidneys, pancreas, heart and brain (MedlinePlus). Cleveland Clinic describes it as an enzyme that helps protect cells from damage. Doctors use GGT mainly to find diseases of the liver and bile ducts, and to answer one specific question: when ALP (alkaline phosphatase) is high, is it coming from the liver or from bone? GGT and ALP rise together with liver and bile duct problems, while bone problems raise ALP without affecting GGT (Cleveland Clinic).

GGT also rises with alcohol and with some medicines, so a raised value is not specific to any one disease.

What high GGT means

MedlinePlus and Cleveland Clinic list these causes of a raised GGT:

• Alcohol: regular heavy drinking, and drinking shortly before the test
• Liver disease: hepatitis, fatty liver, cirrhosis and other liver damage
• Blocked bile flow from the liver
• Other conditions: diabetes, pancreatitis and heart failure
• Medicines: acetaminophen, some seizure medicines such as phenytoin and phenobarbital, and warfarin

A high GGT with a high ALP suggests a liver or bile duct cause rather than bone (Cleveland Clinic). Because alcohol and medicines raise GGT too, a doctor will read it alongside your history and the other liver tests before deciding on any follow-up.

GGT with the rest of the liver panel

These patterns guide the next step; they are not a diagnosis. Your doctor will combine them with your history, and sometimes imaging.

Worked example: GGT of 88 with regular drinking

Say a 52-year-old man who drinks three or four beers most evenings gets a GGT of 88 U/L, an ALT of 38 U/L and an ALP inside his lab's range. His GGT is more than double the MedlinePlus upper limit of 40 U/L and 38 over Cleveland Clinic's typical 50. His ALT is above the ACG healthy limit for men (33 U/L). Because his ALP is normal, the liver-or-bone question does not arise: the GGT itself is the finding.

What might explain it: regular drinking is the obvious candidate, and fatty liver is another common cause on the MedlinePlus and Cleveland Clinic list. Some seizure medicines, warfarin and acetaminophen can also raise GGT.

Questions to take to his doctor:

• Should I repeat GGT and ALT after a stretch without alcohol, and how long should that be?
• Do I need a fuller liver function test or imaging to check for fatty liver?
• Could any of my medicines be raising GGT?

What low GGT means

Neither MedlinePlus nor Cleveland Clinic treats a low GGT as a clinical problem. MedlinePlus notes that birth control pills and clofibrate can lower GGT.

What lowers GGT

• Alcohol: cutting back or stopping is the most direct lever. Cleveland Clinic advises avoiding alcohol for at least 24 hours before the test.
• Weight and blood sugar: fatty liver and diabetes both raise GGT, so the steps that improve A1C and triglycerides usually help.
• Medicines: if a medicine is raising GGT, your doctor may weigh alternatives. Do not stop a prescribed medicine on your own.

GGT blood test: how to prepare

Cleveland Clinic advises no alcohol for at least 24 hours before a GGT test and telling your provider about all medicines and supplements, since many affect the result. It is usually ordered with other liver tests (ALT, AST, ALP and bilirubin). If a result is high, repeat it after a period without alcohol before drawing conclusions.

Cleveland Clinic says doctors typically order GGT when there are signs of liver disease or a blocked bile duct, or to explain a high ALP. As a routine tracking marker it is most useful if you drink regularly, take a medicine known to affect the liver, or already have a raised ALT, because a trend over several tests says more than any single value.

Which at-home tests include GGT

GGT is on two SiPhox panels: Ultimate 360 and GLP Optimization. The four included core panels do not have it, though Heart & Metabolic and Thyroid Focus include ALT and AST.

Both panels include the full liver set: ALT, AST, ALP, total and direct bilirubin and the AST:ALT ratio. Collection is from the upper arm at home, and there is no included doctor review, so take a high GGT to your doctor. GLP Optimization is built for people on GLP-1 medicines (see our GLP-1 blood test page); Ultimate 360 is the broadest panel. The ferritin page covers another marker that rises with liver stress, and our SiPhox review covers the service.

Ultimate 360

$249 + $25 shipping per test

62 biomarkers per test

Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.

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GLP Optimization

$199 + $25 shipping per test

46 biomarkers per test

Built for people on GLP-1 medication: metabolic, liver, kidney, nutrient and iron markers.

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Full liver panel from homeUltimate 360 and GLP Optimization include GGT, ALT, AST, ALP and bilirubin in one needle-free draw.

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