Tartrate Resistant Acid Phosphatase (TRAP) is a test performed on blood cells or bone marrow (biopsy) to support a diagnosis of hairy cell leukemia. This test can also be done on blood plasma, in which case the doctor is looking for signs of bone breakdown, for example to measure bone destruction caused by cancer.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to cause the vein to swell 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 band is removed to restore normal blood flow. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

This test also can be done on a bone marrow biopsy.

No special preparation is needed for the blood test.

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.