A GGT blood test is usually performed to check the levels of GGT, i.e., gamma-glutamyl transferase or gamma-glutamyl transpeptidase, in blood.
Gamma-glutamyl transferase is a protein or an enzyme which occurs in the liver, gallbladder, kidneys, spleen, and pancreas. However, most of GGT present in blood is passed on by the liver. It is responsible for enhancing the metabolic rate of glutathione as well as transmission of peptides and amino acids to the cells of the body.
A GGT test is also helpful in evaluating the precise cause of increased levels of ALP or alkaline phosphatase, which is an enzyme or protein needed for efficient metabolic activities in the body. ALP occurs in different tissues and parts of the body, including the liver kidneys, intestinal wall, bones, bile ducts, and placenta.
Liver diseases and blockages in the bile duct and trigger an increase in the levels of GGT normal range and ALP, while bones disorders cause an increase in the levels of ALP only. When a GGT test results report a higher than normal levels of gamma-glutamyl transferase enzyme, then it is usually an indication that some kind of preexisting condition is harming the health of the liver. The test results however do not specify the exact condition that is causing liver damage.
The GGT blood test: The How, Why, When?
When is the GGT performed?
- The GGT test may be ordered by a doctor if he/she observes high levels of ALP in a patient. The test may be carried out in addition to, or as a follow up to, other kinds of liver enzyme function tests if an individual shows the signs and symptoms of liver damage or liver diseases like:
- Jaundice marked by yellowish hue of the skin and/or the eyes
- Reduced levels of energy; excessive fatigue
- Outflow of urine that is dark in color
- Elimination of stool or feces that is light in color
- Reduced or absent appetite
- Itchy skin
- Vomiting and nausea
- Swelling or pain in the abdomen
How is a GGT test carried out?
- A GGT blood test is typically performed after a person has fasted for a minimum of 8 hours. This is because the GGT levels tend to drop after meals.
- Individuals will be advised to stop the intake of medications which may be taken by the patient on a routine basis. It is so because certain medicines can affect the outcome/results of the GGT test.
- A nurse/doctor will insert a needle attached to a syringe into a vein in the arm and then draw out a sample of blood. This procedure is known as a venipuncture. Most people will experience just a stinging sensation or a prick, while some may feel pain when the skin is punctured with the needle. Later, the affected site is covered with a small tiny strip of bandage to stop any bleeding. Patients may experience some throbbing at the site after the procedure is complete.
- The blood specimen is then taken to a lab for analysis.
Why is the GGT test carried out?
- A GGT test is performed for the following reasons:
- To ascertain an underlying hepatobiliary disease, i.e., high levels of GGT. Hepatobiliary disease is regarded as the most sensitive enzymatic sign of liver disorder.
- To check the presence of bile duct conditions or liver diseases. The GGT test is often carried out along with other diagnostic tests like bilirubin, ALP, and ALT tests; it helps distinguish between underlying bile duct to liver conditions and bone/skeletal abnormalities.
- It may also be performed to check/monitor/screen for occult alcoholism or alcohol abuse.
The GGT test: Risks
Drawing out blood from the arm for a GGT test comes with minimal risk to health problems or complications. The size of the arteries and veins tend to differ from one side of body to another, and from one person to another. Hence, drawing a blood sample from some individuals may be more problematic as compared to some others.
Some of the risks involved are listed below:
- Lightheadedness or fainting
- Bleeding at the site of needle insertion.
- Hematoma, i.e., accumulation or buildup of blood under the surface of the skin.
- In rare cases, the site may develop an infection.
Causes of elevated levels of GGT in blood
It is also important for patients to inform the doctor about different medicines being currently taken by them before the GGT blood test is carried out. This is because the GGT levels tend to rise after intake of certain drugs such as antibiotics, NSAIDs, anti-seizure drugs, antidepressants, and antifungal agents, etc.
The below listed ailments and factors can cause the levels of GGT to become higher than the normal range:
- Obstruction or blockage in the bile duct due to causes such as stones, tumors, etc.
- Dysfunction of the liver or the bile duct; it may occur due to acute damage of the organs.
- Cholestasis, i.e., blockage in the flow of bile from the liver
- Hepatitis, liver necrosis, liver ischemia, liver tumor, and cirrhosis
- Intake of alcohol. It may be noted that the levels of GGT in chronic drinkers are higher than in those who drink occasionally or socially.
- Pancreatic disease
- Congestive heart failure
- Intake of drugs like phenytoin or phenobarbital.
- Lung disease,
Causes of reduced levels of GGT in blood
The below listed ailments and factors can cause the levels of GGT to become lower than the normal range:
- Malfunction of the hypothalamus
- Low levels of thyroid
- Severely decreased levels of magnesium
- Use of drugs like clofibrate and/or birth control pills.
GGT normal range
The GGT normal range levels for adults and children are the same. It may however be noted that the normal range tends to be nearly 5 times higher in newborns as compared to that of an adult. Also, the GGT normal range values tend to differ from one lab to another. Hence, consult a doctor for interpretation and understanding the results of a GGT test.
Presented below is a table detailed the GGT normal range
|Description||GGT level in international units per liter (U/L)|
|Normal adult male range||0 to 65 U/L|
|Normal adult female range||0 to 65 U/L|
|High GGT for women and men older than 45 years||GGT > 38 U/L|
|High GGT for women who are younger than 45 years||GGT > 27 U/L|