Prostate-Specific Antigen (PSA) Test
Prostate-specific antigen (PSA) is a substance that the prostate makes that is added to semen that makes it more fluid to help carry sperm and to aid ejaculation. It is normally present in the blood in only very small amounts because there is a good prostate-blood barrier in the absence of prostate problems. The PSA test measures levels of PSA in the blood. This is the best available marker for prostate cancer because cancer interrupts the barrier between prostate and blood, so levels in the blood increase. This is the earliest indication of cancer. The limitation of the test is that cancer is not the only thing that increases PSA levels. When the prostate gland enlarges with age (benign prostatic hyperplasia, or BPH), more PSA is produced and more gets into the blood. Other conditions, notably inflammations of the prostate, can disrupt the prostate-blood barrier and result in elevated blood PSA levels. Scientists are studying ways to improve the ability of the PSA test to target cancer.
