Free prostate-specific antigen 'in the field': a useful adjunct to standard clinical practice.

Objectives: To determine the clinical utility of the ratio of free to total prostate-specific antigen (f/tPSA), which may improve the discrimination of PSA testing in the assessment of patients with prostatic disease, in a busy clinical practice.

Patients And Methods: A series of 198 men undergoing transrectal ultrasonography (TRUS)-guided biopsy, because of a high total PSA level or an abnormal digital rectal examination or both, had blood samples taken for the assessment of both free and total PSA before any form of prostatic manipulation. The histological findings were compared with tPSA, fPSA and f/tPSA, evaluating three different thresholds of f/tPSA.

Results: PSA levels, PSA density and fPSA density differed significantly between those with benign histology and neoplasia. The f/tPSA only differed significantly in men with a PSA level of 10. 1-15 ng/mL. The f/tPSA threshold of 0.25 was the most useful clinically, with a negative predictive value for prostate cancer of 91%. Using this threshold would reduce the negative biopsy rate by 30%.

Conclusion: The f/tPSA is of clinical value in reducing the negative biopsy rate and in the management of patients with a high PSA level and previous negative biopsies.