Gamma-glutamyl transferase, commonly known as GGTP or GGT, is an enzyme found throughout the body, with its highest concentrations in the liver and bile ducts. A routine blood test evaluates its presence in the blood, serving as a general indicator of liver health.
What the GGTP Test Measures
The GGTP test measures the level of gamma-glutamyl transpeptidase in the blood. Doctors often order this test to screen for liver diseases, investigate symptoms like jaundice, fatigue, or abdominal pain, or to assess for bile duct obstruction. It also monitors liver health in individuals with conditions that might affect the liver, including those with a history of alcohol use.
The GGTP test involves a simple blood draw from a vein in the arm. Fasting for at least eight hours before the test is recommended. Avoiding alcohol consumption for at least 24 hours prior is also advised, as even small amounts can temporarily elevate GGTP levels. Patients may also be instructed to temporarily stop certain medications that can influence GGTP levels, such as specific anticonvulsants or NSAIDs.
How GGTP Levels Are Interpreted
Normal GGTP levels vary slightly depending on the laboratory, age, and sex. For adult males, a normal range is often 7 to 47 units per liter (U/L), while for adult females, it is typically 5 to 25 U/L. Some laboratories may cite a broader normal range, such as below 50 U/L for adults. Newborns typically have higher GGTP levels compared to adults.
Elevated GGTP levels generally indicate potential liver damage, issues with the bile ducts, or recent alcohol consumption. Higher levels suggest more extensive suspected liver damage. However, GGTP is a sensitive but non-specific marker, meaning it signals a problem but does not pinpoint the exact cause. An elevated GGTP result therefore necessitates further investigation.
Low GGTP levels are less common and typically do not hold significant clinical meaning in isolation, generally suggesting the absence of liver dysfunction or recent alcohol intake. Interpreting GGTP results is best done in conjunction with other liver enzyme tests, such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP), as well as a patient’s overall health picture. For instance, if ALP is high but GGTP is normal or low, it suggests a bone disorder rather than a liver issue.
Common Causes of Elevated GGTP
Elevated GGTP levels can stem from various conditions affecting the liver and other organs. Liver diseases are a common source, including alcoholic fatty liver disease and non-alcoholic fatty liver disease (NAFLD/NASH), which involves fat accumulation in the liver. Viral hepatitis, such as types A, B, and C, and autoimmune hepatitis, where the body’s immune system attacks liver cells, can also lead to increased GGTP. More advanced liver conditions like cirrhosis, characterized by scarring of the liver, and liver cancer are also associated with higher GGTP levels.
Bile duct issues frequently cause GGTP elevation because the enzyme is highly concentrated in these ducts. Obstructions from gallstones, inflammation of the bile ducts (cholangitis), or tumors that block bile flow can all lead to a rise in GGTP. The GGTP test is particularly sensitive for detecting bile duct problems, often being the first liver enzyme to rise in such cases.
Alcohol consumption is a well-known and frequent cause of elevated GGTP. Chronic alcohol use directly affects liver cells, leading to increased enzyme production and leakage into the bloodstream. Even modest alcohol intake within 24 hours before a test can temporarily raise GGTP levels. GGTP is often used to screen for and monitor alcohol use disorder.
Certain medications can also elevate GGTP levels as a side effect. Examples include some anticonvulsants like phenytoin and phenobarbital, statins used for cholesterol management, and certain antibiotics. Other medical conditions can also be associated with elevated GGTP, though less directly linked to liver damage. These include heart failure, diabetes, pancreatitis, hyperthyroidism, and obesity.
What to Do After an Abnormal GGTP Result
An abnormal GGTP result requires prompt consultation with a healthcare professional. Avoid self-diagnosis, as GGTP is a general indicator, not a definitive diagnosis. Your doctor will consider your medical history, symptoms, and other test results to understand the complete picture.
A doctor might order additional liver function tests, such as bilirubin and albumin, to assess overall liver function. Imaging studies, including an ultrasound, CT scan, or MRI of the abdomen, may be recommended to visualize the liver and bile ducts for abnormalities like blockages or structural changes. Specific tests for viral hepatitis or autoimmune conditions might also be performed if suspected.
Lifestyle modifications are often recommended to help normalize GGTP levels, especially if alcohol consumption or fatty liver disease is a contributing factor. This includes reducing or eliminating alcohol intake and adopting dietary changes to support liver health, such as a balanced diet low in processed foods and saturated fats. Weight management through diet and exercise is also beneficial, particularly for individuals with non-alcoholic fatty liver disease.