The variation of percent free prostate-specific antigen determined by two different assays.

BACKGROUND

We evaluated the difference in values of the percent free Prostate-specific antigen (PSA) as measured by the Hybritech Tandem R assay (USA) and the Cis bio international assay (France).

MATERIALS AND METHODS

A total of 99 patients scheduled for transrectal ultrasonography (TRUS) of the prostate and sextant biopsy were subjected to measurements of total and free PSA using the Hybritech Tandem R assay and the Cis bio international assay with the same serum sample.

RESULTS

Thirty patients were confirmed to have prostate cancer and 69 patients to have benign prostate hyperplasia (BPH). The Pearson coefficients of correlation of the Cis bio international assay versus the Tandem R assay were 0.979 for total PSA, 0.987 for free PSA and 0.937 for percent free PSA. The mean total PSA measured by Tandem R was 8.65 +/- 5.36 ng/ml, which was significantly higher than those determined by Cis bio international assay, 7.60 +/- 4.46 ng/ml (p < 0.0001). The mean free PSA determined by Tandem R assay was 1.47 +/- 1.01 ng/ml, which was significantly less than that measured by Cis bio international assay, 1.75 +/- 1.18 ng/ml (p < 0.0001). Thus the percent free PSA calculated by the Cis bio international assay also had significantly higher mean values compared to the Tandem R assay (24.08 +/- 10.09 vs. 18.22 +/- 8.17, p < 0.0001).

CONCLUSION

The optimal cut-off value of percent free PSA for biopsy reference was demonstrated to be higher when determined by Cis bio international assay than Tandem R assay.