Critical aspects related to the interpretation of the free-to-total PSA-ratio.

INTRODUCTION

The number of assays available for the measurement of total and free PSA is increasing. As different methods can determine different PSA concentrations as well as different free-to-total PSA ratios in identical serum samples, the cut-offvalue for the ratio still needs to be determined.

METHODS

114 sera from patients with histologically confirmed benign prostatic hyperplasia (BPH; n = 58) and cancer of the prostate (CaP; n = 56) were analyzed with two different assays. Free PSA (free), total PSA (total) and the free-to-total- PSA ratio (ratio) were determined employing Enzym-Test PSA und freies PSA (Boehringer Mannheim, Germany) and Immulite PSA und freies PSA (DPC Biermann, Bad Nauheim, Germany)

RESULTS

The statistical results are tabulated below: [table: see text]

CONCLUSION

Direct comparison of the two assays revealed a high statistical correlation (r = 0.94-0.99) for free and total PSA. In contrast, the ratio of the two assays was not as reproducible (r = 0.81-0.83). This result indicates that the reference range for the ratio is dependent on the assay employed and an that uncritical use of an applied reference range can be counter-productive.