PSA Test
(Prostate Specific Antigen)

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Prostate specific antigen (PSA) facts

What is prostate specific antigen (PSA)?

Prostate specific antigen (PSA) is a substance produced almost exclusively by certain cells within the prostate gland. Biochemically, it belongs to the protease family of kallikrein and is also known as human kallikrein 3 (hK3). PSA is secreted by the prostate in the semen where its role is to liquefy the semen following ejaculation. Most of the PSA produced by the prostate gland is carried out of the body in semen, but a very small amount escapes into the blood stream, so PSA is normally found in low amounts (nanograms per milliliter or ng/mL) in the blood.

If the PSA level is high for your age or is steadily increasing (with or without an abnormal physical exam), a biopsy may be recommended. The doctor should consider other risk factors of prostate cancer such as family history and ethnicity before recommending the biopsy. The biopsy is the only way to determine if prostate cancer or other abnormal cells are present in the prostate.

How is PSA measured?

PSA is measured by a blood test. Since the amount of PSA in the blood is very low, detection of it requires a very sensitive type of technology (monoclonal antibody technique). The PSA protein can exist in the blood by itself (known as free PSA), or bound with other substances (known as bound or complexed PSA). Total PSA is the sum of the free and the bound forms. The total PSA is what is measured with the standard PSA test.

Medically Reviewed by a Doctor on 11/3/2015

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