Value of free prostate-specific antigen (Hybritech Tandem-R) in symptomatic patients consulting the urologist.

INTRODUCTION: Prostate-specific antigen (PSA) is a widely used tumor marker in the detection and follow-up of adenocarcinoma of the prostate. Selection of candidates for prostate biopsies is hampered by the lack of specificity resulting in a large number of unnecessary biopsies. The intention of our study was to compare the percent free PSA (f-PSA; Hybritech Tandem-R) with total PSA and age-specific PSA reference values to evaluate the clinical benefit in detecting patients with prostate cancer (PC) in a selected group of patients consulting the urologist. The question was whether cutoff points are influenced by this selection of patients.
METHODS: A total of 188 patients, 114 with benign prostate hyperplasia (BPH) and 74 with PC were selected. It is a selected group of patients consulting the urologist. Diagnosis was confirmed in the BPH and PC groups by either ultrasound-guided biopsy or transurethral resection of the prostate or suprapubic adenomectomy or cystoprostatectomy. Total PSA (t-PSA) and f-PSA of all patients were measured before any manipulation by Tandem-R assay for f-PSA and Tandem-E assay for t-PSA (Hybritech). Mean values of age, prostate volume, t-PSA, f-PSA, percent f-PSA were compared in patients with BPH and PC by Mann-Whitney U test. The sensitivity and specificity of t-PSA and age-specific PSA were compared to the sensitivities and specificities of different cutoff points of percent f-PSA.
RESULTS: The mean value of t-PSA, f-PSA and percent f-PSA in patients with BPH (n = 114) and PC (n = 74) were statistically significantly different. At PSA levels between 4 and 10 ng/ml 19% of negative biopsies could be avoided by the use of percent f-PSA (cutoff point 25%). There was no additional benefit of age-specific PSA. At a PSA of <4 ng/ml 6 of 7 PCs could be diagnosed by percent f-PSA (cutoff point 25%), whereas only 1 patient would be diagnosed by age-specific PSA.
CONCLUSION: Percent f-PSA seems to decrease the biopsy rate at PSA levels from 4 to 10 ng/ml without missing a relevant number of cancers and to increase the detection rate at PSA <4 ng/ml. Our data indicate that it might be necessary to choose high cutoff points (25%; Tandem-E and R assay, Hybritech) in a selected study population consulting the urologist with large glands and a high prevalence of disease. However, this situation is not comparable to testing of screening populations. No benefit of age-specific PSA could be observed in this study. Copyright 2000 S. Karger AG, Basel