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.

Tartrate-resistant acid phosphatase (TRAP) is a different form of the enzyme acid phosphatase, which is found mainly in bone and some blood cells. TRAP has a different physical structure than acid phosphatase, but it speeds up (catalyzes) similar kinds of chemical reactions in the body.

Hairy cell leukemia is a type of blood cancer in which TRAP levels are very high. To help diagnose hairy cell leukemia, a stain for TRAP on leukemia cells in the blood or bone marrow can be performed. If this test is negative, the diagnosis is not likely to be hairy cell leukemia.

TRAP is also released during the activity of cells that break down bone (osteoclasts). Any condition in which bone is broken down faster than usual may lead to high levels of TRAP in the blood. In this case the TRAP is not contained within the blood cells, but is free in the liquid part of blood (plasma).

Measuring TRAP in the plasma can follow the activity of cancers that invade bone. These cancers include multiple myeloma, and breast, lung, or prostate cancer which has spread (metastasized) to bone. The TRAP test is not yet widely used for these conditions, but it may be used more in the future if research proves it to be useful.

There should be less than 5 ng/ml of acid phosphatase in the presence of tartrate.

Note: ng/ml = nanogram per milliliter

A high level of TRAP in leukemia cells supports a diagnosis of hairy cell leukemia.

A high level of TRAP in the plasma indicates bone breakdown. This can be due to many types of diseases, but in a patient with cancer it likely indicates that the cancer has spread to bone.

• Excessive bleeding
• Fainting or feeling light-headed
• Blood accumulating under the skin (hematoma)
• Infection
• Multiple punctures to find veins

This test is less often used to diagnose hairy cell leukemia because now there is a method to identify cells based on types of markers found on the cell surface (immunophenotyping).