TRAP - Tartrate Resistant Acid Phosphatase

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This is a test performed on blood cells or bone marrow (biopsy) in order 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.

Type 5 acid phosphatase

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 circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Alternatively, the test can be done on a bone marrow biopsy. This test is discussed in detail in another section.

No special preparation is necessary 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 an isoenzyme of acid phosphatase which is found mainly in bone and some blood cells. Isoenzymes are different forms of an enzyme with different physical structures, but which catalyze (speed up) similar biochemical reactions. Isoenzymes frequently differ in concentration in different tissues.

Hairy cell leukemia is a type of blood cancer in which TRAP levels have been found to be very high. A stain for TRAP on leukemia cells in the blood or bone marrow can help support a diagnosis of hairy cell leukemia. If this test is negative, the diagnosis of hairy cell leukemia is unlikely.

TRAP is also released during the activity of osteoclasts, a type of cell that breaks down bone. Because of this, any condition in which bone is broken down faster than usual may lead to excessive levels of TRAP in the blood. In this case the TRAP is not contained within the blood cells, but is free in the plasma, the liquid part of blood.

The activity of cancers that invade bone, such as multiple myeloma, and breast, lung or prostate cancer which has metastasized to bone, can be followed by measuring TRAP in the plasma. This test is not yet in widespread use for these conditions, but it may be used more in the future if research proves it to be useful.

Review Date: 07/29/2005
Reviewed By: William Matsui, M.D., Assistant Professor of Oncology, Division of Hematologic Malignancies, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD. Review provided by VeriMed Healthcare Network.