Gamma-Glutamyl Transferase, or GGT, is an enzyme that is frequently measured as part of routine blood work to assess overall health. This enzyme is found in low concentrations in the bloodstream, and its presence is a common marker utilized by medical professionals. Measuring the level of GGT in the blood helps in the evaluation of various physiological processes within the body. An elevated GGT result often suggests that a condition is causing cellular stress or damage.
The Biological Role of GGT
Gamma-Glutamyl Transferase is a protein that functions as a transferase enzyme, meaning it helps move chemical groups between molecules within the body’s cells. The enzyme is integral to the gamma-glutamyl cycle, a pathway responsible for the synthesis and breakdown of glutathione. Glutathione is a tripeptide that operates as the body’s primary water-soluble antioxidant, protecting cells from damage caused by free radicals.
GGT’s specific function involves transferring a gamma-glutamyl group from molecules, like glutathione, to an acceptor molecule, such as an amino acid. By breaking down extracellular glutathione, GGT helps to provide cysteine, a component required for the cell to manufacture new glutathione internally. While GGT is found in numerous tissues, the highest concentrations are located in the kidney, pancreas, and the cells that line the bile ducts and liver. However, the GGT that circulates in the blood primarily originates from the hepatobiliary system, making it a valuable biomarker for function in that region.
Purpose of the GGT Blood Test
The GGT blood test is most often ordered to evaluate potential issues related to the liver or bile ducts. Measuring the enzyme level in the blood acts as a sensitive indicator that cell damage or stress is occurring within the hepatobiliary system. Although GGT is highly sensitive to liver changes, it is typically not used alone to pinpoint a specific diagnosis, but rather as part of a panel of liver function tests.
A significant application of the GGT test is to help distinguish the source of an elevated Alkaline Phosphatase (ALP) result. ALP can be elevated due to either liver or bone disorders, but GGT levels are not affected by bone issues. If both GGT and ALP are elevated, it strongly suggests the problem originates in the liver or bile ducts. Conversely, if ALP is high but GGT remains within the normal range, the elevation is likely due to a bone condition. The test is also used to monitor the progression of known conditions that affect the liver or to assess the effectiveness of treatment for those conditions.
Understanding Elevated GGT Results
An elevated GGT level in the blood indicates that the enzyme is leaking from damaged cells, most commonly from the liver. While it does not specify the exact cause of the injury, the elevation is suggestive of liver stress or bile duct obstruction. GGT is often the first enzyme to rise when the bile ducts are blocked, such as by gallstones or a tumor.
Several liver diseases can cause GGT to rise, including hepatitis (inflammation of the liver) and cirrhosis (scarring of the tissue). Non-alcoholic fatty liver disease, a growing concern often linked to metabolic syndrome, is also a common cause of GGT elevation. Certain prescription medications, such as some anti-seizure drugs and acetaminophen, can induce liver stress and temporarily increase GGT levels.
GGT is particularly well-known as a sensitive marker for heavy alcohol consumption. In individuals who regularly drink excessive amounts of alcohol, GGT levels are frequently elevated, sometimes significantly. GGT may be used to monitor abstinence in individuals receiving treatment for alcohol use disorder, as the enzyme levels will slowly decrease over several weeks without further consumption. High GGT levels have also been associated with other conditions not directly related to the liver, such as congestive heart failure, diabetes, and metabolic syndrome, suggesting a link to systemic oxidative stress.
Next Steps After Abnormal Findings
Following an elevated GGT result, a healthcare provider will typically order additional tests to identify the precise source of the elevation. This usually includes a complete liver panel, measuring other liver enzymes like Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST), along with bilirubin levels. The pattern of these enzymes can offer more specific clues regarding the type of liver injury present.
In some cases, the medical evaluation may involve imaging studies, such as an abdominal ultrasound, to visualize the liver and bile ducts for signs of obstruction or structural changes. If no immediate explanation is found, the provider will thoroughly review the patient’s medical history, including medication use and alcohol intake. Depending on the suspected cause, lifestyle modifications, such as reducing alcohol consumption, adjusting diet, or changing medications, may be recommended to help normalize GGT levels.