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How Stable Are Serum PSA Levels?
Researchers assessed the risk for false-positive results of prostate-specific antigen testing in healthy men.
The use of serum prostate-specific antigen (PSA) levels to screen for prostate cancer is controversial because of the difficulty in differentiating clinically insignificant cancers from those that require definitive, but potentially harmful, treatments. Risk that a single PSA determination might yield a false-positive indication of prostate cancer was studied retrospectively. Five blood samples were collected during a 4-year period from each of 972 healthy men (age range, 35-89; median, 62) who were enrolled in an unrelated study.
Evaluated criteria for identifying abnormally elevated PSA levels were total PSA level, age-specific PSA level, free-to-total PSA ratio, and PSA velocity: 361 men (37%) would have had positive results by at least 1 criterion during 4 years. At least 15% would have met any single criterion. Among men with abnormal levels by any criterion (except PSA velocity), 40% to 55% of those who did not develop documented prostate cancer in the interim exhibited subsequent normal values.
Comment: The authors recommend a policy of repeating abnormal PSA tests in 4 to 6 weeks to reduce the risk for false-positive results. Many practitioners also prescribe broad-spectrum antibiotics during that waiting period, on the assumption that abnormal results might be caused by prostatitis. However, such precautions do not address the larger issue of whether the natural history and clinical outcomes of prostate cancer in large, unselected populations are improved at all by PSA screening.
— Thomas L. Schwenk, MD
Published in Journal Watch General Medicine June 20, 2003
Citation(s):
Eastham JA et al. Variation of serum prostate-specific antigen levels: An evaluation of year-to-year fluctuations. JAMA 2003 May 28; 289:2695-700.
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