DefinitionTartrate resistant acid phosphatase (TRAP) is a test performed on blood cells or bone marrow (biopsy) to confirm a diagnosis of hairy cell leukemia. This test can also be done on blood plasma to look for signs of bone breakdown.Alternative NamesType 5b acid phosphatase test; TRAP testHow the test is performedBlood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.O