Gamma-glutamyltransferase, also known as GGT, is an enzyme that is found mainly in the liver. But it may also be found in the:
GGT levels are measured when a doctor suspects there is damage or disease in the liver or the biliary system.
In order to measure the amount of GGT in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube called a tourniquet is tied around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.