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Complexed PSA Test Shows Improved Specificity over Total PSA: Presented at AUA

By Emma Hitt
Special to DG News

ORLANDO, FL -- May 28, 2002 -- Measuring complexed prostate specific antigen appears to provide improved specificity over total PSA (tPSA), according to results of a multicenter trial. presented at the annual meeting of the American Urological Association (AUA) in Orlando, Florida.

PSA exists in two forms in the blood: free prostate specific antigen, which is not bound to protein, and complexed prostate specific antigen (cPSA), which is bound. Total prostate specific antigen (tPSA) is the measurement of free and complexed PSA.

In their study, Dr. Alan W. Partin, professor of urology, Johns Hopkins University, Baltimore, Maryland, United States, and colleagues compared the clinical performance of a cPSA test as a first-line test for detecting prostate cancer versus a standard tPSA test and PSA ratios (percent free PSA and percent cPSA).

A total of 831 consecutive men scheduled for prostate biopsy were enrolled for the study at seven evaluation sites. Biopsy determined that 37.5 percent of the men had cancer.

PSA testing was conducted with Bayer Immuno 1 tPSA and cPSA assays and Beckman Access free and tPSA assays.

An analysis performed from results of all samples, and those within the clinically relevant tPSA ranges of 4 ng/mL to 10 ng/mL, and 2 ng/mL to 6 ng/mL indicated a statistically significant improvement in the detection ability of cPSA in comparison with tPSA (p<0.003), the researchers found.

In 604 men with tPSA levels of 2 ng/mL to 10 ng/mL, when sensitivity was 95 percent, a specificity of 18 percent was achieved with the cPSA test compared with a specificity of 14 percent with the tPSA test.

Measuring percent free PSA and percent cPSA provided no further enhancement in specificity over cPSA, they report.

The researchers conclude that "cPSA outperforms tPSA over all PSA ranges and can be used as a first-line test for prostate cancer detection."

"Previous assays require measurement of complexed PSA and free PSA, so the real advance is to measure the complexed PSA with a single assay," study co-author Dr. Herbert Lepor, with the New York University School of Medicine, New York, New York, said in an interview with Doctor's Guide.

"Having an assay that decreases the number of false negatives by being more specific is attractive, especially since there is no cost difference," he said.

The study was funded by Bayer Diagnostics, of Tarrytown, New York.

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