Prostate specific antigen

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Prostate specific antigen (PSA, also known as kallikrein III, seminin, semenogelase, γ-seminoprotein and P-30 antigen) is a protein manufactured almost exclusively by the prostate gland; PSA is produced for the ejaculate where it liquifies the semen and allows sperm to "swim" freely. It is also believed to be instrumental in dissolving the cervical mucous cap, allowing the entry of sperm.

Biochemically it is a serine protease (Template:EC number) enzyme, the gene of which is located on the nineteenth chromosome (19q13).

Higher than normal levels of PSA are associated with both localized and metastatic prostate cancer (PCa). PSA is normally present in the blood at very low levels. Increased levels of PSA may suggest the presence of prostate cancer. However, prostate cancer can also be present in the complete absence of an elevated PSA level, in which case the test result would be a false negative. PSA levels can be also elevated due to prostate infection, irritation, benign prostatic hypertrophy (enlargement) or hyperplasia (BPH), recent ejaculation, digital rectal exam etc., in which case it may give a false positive. Recent research suggests that the rate of increase of PSA (the "PSA velocity") may be a more specific marker for prostate cancer.

The U.S. Food and Drug Administration (FDA) has approved the PSA test for annual screening of prostate cancer in men of age 50 and older. PSA levels between 4 and 10 ng/mL (nanograms per milliliter) are considered to be suspicious and should be followed by rectal ultrasound imaging and, if indicated, biopsy. PSA is false positive-prone (7 out of 10 men in this category will still not have prostate cancer) and false negative-prone (2.5 out of 10 men with no elevation in PSA will have prostate cancer)Template:Ref.

The current guidelines of the American Cancer Society recommend that non-African American men over age 50 should be "offered" a prostate exam every year. African-American men and those with a family history of prostate cancer should be screened annually upon reaching 40 years. These guidelines may be changing. A new European study has shown that a thorough screening for prostate cancer every 4 years is adequate. The screening comprises a PSA blood test, a digital rectal exam, and a transrectal ultrasound. "Very few, if any, aggressive prostate cancers escape (this) screening."

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Reference

Template:Note Thompson IM, Pauler DK, Goodman PJ, Tangen CM, Lucia MS, Parnes HL, Minasian LM, Ford LG, Lippman SM, Crawford ED, Crowley JJ, Coltman CA Jr. Prevalence of prostate cancer among men with a prostate-specific antigen level < or =4.0 ng per milliliter. N Engl J Med 2004;350:2239-46. PMID 15163773.

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