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How effective is a PSA test for detecting prostate cancer?

Although the prostate-specific antigen (PSA) test is not perfect, it is the best currently available test for early detection of prostate cancer. Since doctors started using the test, the number of prostate cancers found at an early, curable stage has increased. Because most men have normal test results, they can be reassured that they are unlikely to have prostate cancer, especially if the digital rectal exam (DRE) is also negative.

While the PSA test is considered a major advance in diagnosing early-stage prostate cancer, it has some drawbacks. For 100 men over 50 at average risk for prostate cancer, the following would be found if they all had a PSA test:

  • Ten of the 100 men would have a PSA level higher than normal (over 4.0). The 10 men would need further testing to clarify their abnormal levels.
  • Three of the 10 men would be found to have prostate cancer.
  • Seven of the 10 men would be found not to have prostate cancer. They would have an elevated PSA for other reasons—most likely benign prostatic hyperplasia (BPH).
  • Ninety of the 100 men would have PSA levels in the normal range (<4.0).
  • One or two of these 90 men would be found to have significant prostate cancer that becomes life threatening.

This shows that the PSA test is moderately sensitive. Of 100 men with prostate cancer, it will detect only about 70 of them, a sensitivity of about 70 percent. But the positive predictive value of the PSA test is low. Only three out of 10 positive results were cancer (PPV of about 30 percent). And seven out of 10 positive PSA results (i.e., greater than 4.0) are false-positive results; this means that two out of three men who are told that they may have cancer after taking the PSA test actually do not have it. When the PSA is greater than 10.0, the test is more accurate. There is about a 50-50 chance of having cancer at this level of PSA.

Negative predictive value is high reflecting the low likelihood of having significant prostate cancer with a normal PSA level (NPV of about 98 percent).

The major challenge (for PSA testing), is to identify the cases that need to be treated while avoiding diagnosing patients who will not benefit from being diagnosed and who will only suffer from:

  • the stigma of being a cancer patient.
  • possible consequences/complications of overtreatment.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.