How reliable is the prostate-specific antigen (PSA) test when it comes to detecting prostate cancer?
Kevin R. Loughlin, M.D., M.B.A., director of Urologic Research at Brigham and Women’s Hospital, responds:
Although PSA testing can help catch prostate cancer at an early stage, having an elevated PSA (generally considered more than 4 ng/ml) doesn’t necessarily mean that a man has cancer. Noncancerous conditions, including benign prostatic hyperplasia (BPH), or an enlarged prostate, and prostatitis, can raise PSA levels. In fact, studies have shown that about 70% to 80% of men with an elevated PSA who have a biopsy do not have cancer. However, many men undergo an ultrasound and prostate biopsy, to be certain.
Conversely, the PSA test doesn’t detect all cancers. About 20% of men who have cancer also have a normal PSA (less than 4 ng/ml), so the test may give some men a false sense of security. For this reason, some experts take a man’s age into account when considering a PSA level. And most doctors observe how a man’s PSA level changes over time, a measure called PSA velocity, rather than using it as a one-time indicator. PSA scores tend to rise more rapidly in men with cancer than in those with BPH, for example.
Some doctors also measure the level of free PSA. The PSA protein circulates in the blood in two forms: bound to other proteins or unbound (free). Several studies suggest that men with elevated PSA levels and a very low percentage of free PSA are more likely to have prostate cancer than a benign condition. Knowing your free PSA level won’t give you a definitive answer about cancer, but it may be useful when considering whether a biopsy is an appropriate next step.
Researchers are developing new screening tests for prostate cancer. Like the PSA test, they rely on biomarkers, such as antigens or proteins, which are elevated or may only be present in men who have prostate cancer. The hope is that these tests will better detect existing cancers without raising the alarm for cancer when it isn’t there.
Originally published November 2009; last reviewed March 16, 2011.