DALLAS - A new study has found no clear "normal" level for a PSA test, a finding likely to add to growing uncertainty over one of the foundations of prostate cancer screening.
Doctors had once hoped that blood tests for prostate-specific antigen, or PSA, a substance made normally in a man's prostate gland, could signal when the prostate had turned malignant.
Since the introduction of the PSA test two decades ago, most doctors have settled on a benchmark of 4 nanograms of PSA per milliliter of blood as the warning point for a PSA test. Receiving results above that level, many doctors advise a biopsy of the prostate.
But the number appears to have little meaning, according to the new study, published today in the Journal of the American Medical Association.
The study is the latest in a series that questions the value of the test, which has become almost routine in older men's physical exams. About three-fourths of men over age 50 are believed to have had their PSA levels checked, although studies have not yet demonstrated that PSA screening has lowered prostate cancer mortality.