Question marks rise over the effectiveness of the prostate specific antigen or PSA, the most commonly used diagnostic tool for prostate cancer.

According to the latest recommendation coming from the American Cancer Society, men over 50 have to get a manual rectal exam, followed by a blood test to screen for prostate cancer.

Researchers at New York Presbyterian Hospital of the Weill Medical College of Cornell University concluded that changes in biopsy practices over the years have diminished the PSA’s value in predicting prostate cancer. The technique has been widely used for nearly two decades to screen for prostate cancer, and numerous studies have supported the use of the simple blood test as a predictive test for the cancer. However, that was happening back in the mid 1990s before major changes in prostate biopsy practices.

Before 1990s, biopsies were rarely performed on men with PSA levels lower than 4, whereas today men with PSAs as low as 2.5 are urged to undergo a biopsy. Changes in biopsy practices (taking more core samples from the prostate) have also led to more cancers being found at earlier stages. The problem is that not every man with a high PSA level has prostate cancer, and not every man with Prostate cancer has a high PSA level.

“In men with an abnormal digital rectal examination, it [the PSA test] still is very predictive. For men with a normal digital rectal examination, it has lost the predictive accuracy it had in the 1990s,” said study author Dr. Douglas S. Scherr, clinical director of urological oncology at Weill Cornell Medical Center in New York City

Doctors associated with this study said they urgently need a more effective test than PSA. However, they, and critics, are quick to add that for the time being, PSA is the best cancer-diagnosing tool available.

The study is published in the March 15 issue of the American Cancer Society (ACS) journal Cancer.