Common Questions: The Prostate
What is the prostate PSA test? Why is it used in prostate cancer detection?
PSA prostate specific antigen is a protein produced by the cells of the prostate that form the liquid secreted by the prostate during ejaculation. Prostate-specific antigen is also produced to lower concentrations in other types of cells in the body. Prostate-specific antigen is found in very high concentrations in the ejaculate, but normally only a small portion seems to leak into the bloodstream.
The concentration of PSA prostate-specific antigen in the blood provides an estimate of prostate cancer risk, which provides the rationale for prostate PSA tests in men without symptoms of prostate cancer. In this context, we say that PSA is used in prostate cancer detection.
Numbers matter and patients should not be satisfied with reports of "normal" PSA results. For instance, a prostate-specific antigen concentration between 2.5 and 10.0 ng/ml is associated with a probability of prostate cancer on a prostate biopsy of approximately 25%.
Infections, medications, and other factors can cause fluctuations in the blood concentrations of prostate-specific antigen. Accordingly, prostate-specific antigen is not a diagnostic test. PSA as a test for early detection is done with digital rectal examination (DRE). Prostate cancer diagnosis requires biopsy.