Prostate-specific antigen (PSA) is a protein. It circulates in the blood and usually binds to other larger proteins. The amount of PSA that is not attached to other proteins is called free PSA. Attached protein is called bound PSA.

The standard PSA test measures the total amount of PSA, both free and bound. Some researchers think that men with prostate cancer have more bound PSA than free PSA compared with men who do not have prostate cancer.

Who is a candidate for the test?

Men who have a high standard PSA level, a normal rectal exam and normal prostate biopsy results are candidates for this test.

How is the test performed?

In order to measure the amount of free PSA in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet", is wrapped around the upper arm to enlarge the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn; the puncture site is covered for a short time to prevent bleeding.