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.

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I enjoyed reading this informative and well structured article. Everyone involved in neonatal screening-in hospital and clinical practice and in the laboratory-would be well advised to have this review article and its practical tables ready to hand. I do not think, however, that the positive predictive value reported by the authors on page 16 for the immuno chemical 17-OH progesterone screening (3%), can be deduced from the authors' data on the specificity (adrenogenital syndrome [AGS] 99.39%, page 16) and the confirmed cases (AGS: 216) or the incidence (1:12 771) in Table 1 on page 14; and neither can it be concluded from the cited bibliographical source (2). The positive predictive value for AGS screening can therefore be assumed to be in the region of 1.3%, which means that about 80 (rather than 30) neonates would have to be examined in order to identify one baby with the syndrome.