TRAP (Tartrate Resistant Acid Phosphatase)

Alternative names:

prostate specific acid phosphatase; prostatic acid phosphatase, prostatic ACP

How the test is performed:

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in air-tight vials or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

How to prepare for the test:

No special preparation is necessary.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

Elevated ACP is seen in about three-quarters of patients with prostatic cancer that has metastasized.

Isoenzymes are different forms of an enzyme with slightly different physical structure, but which still catalyze the same biochemical reactions. Isoenzymes frequently differ in concentration in different tissues. Dysfunction of various tissues can be determined by measuring isoenzymes specific to that tissue in the serum. This is because damaged tissue often releases enzymes into the blood.

The prostate normally contains high levels of acid phosphatase (ACP). However, the enzyme is not released into the blood unless there is some dysfunction of the prostate gland. When ACP levels in the blood are increased, the prostate gland is one potential source. However, other tissues such as red blood cells also release ACP into the bloodstream (especially if a hemolytic process is present). The ACP isoenzyme from the prostate (prostate specific acid phosphatase) can be distinguished from the ACP that comes from red blood cells and most other tissues. This is possible because prostatic ACP is inhibited by tartrate (it does not work as well) in contrast to red blood cell ACP, which is not inhibited by tartrate.