The f/t-PSA ratio in diagnosis of in-patients and out-patients: a unitary cutoff value is not useful

Purpose In the prostate specific antigen (PSA) range of 4–10 ng/ml after a negative digital rectal examination, the PSA value indicates a lack of specificity with a carcinoma detection rate of roughly 20%. To improve the biopsy/carcinoma ratio, the interdisciplinary consensus recommends free PSA (fPSA) measurement. This does not take into account the pre-analysis when the cutoff value is established for biopsy indication. Methods In the present study, an in-patient cohort whose blood samples were immediately analysed was compared with an out-patient cohort whose sample processing was delayed by between 24 and 48 h. Results The in-patient cohort comprises 382 patients with 99 prostate carcinomas, the out-patient cohort 987 patients with 235 carcinomas. In the in-patient cohort a sensitivity of 90% with a cutoff value of 25% for the f/t-PSA ratios is achieved with the theoretical possibility of reducing the number of punch biopsies by 34.6%. A sensitivity of 90% in the out-patient cohort necessitates a cutoff value of 18% for the f/t-PSA ratios. The specificity is 35.3% with a possible biopsy reduction of 29.1%. Conclusions The cutoff values from cohorts with an immediate fPSA measurement cannot be adopted for a typical out-patient cohort whose analyses are delayed. On the contrary, an individual adjustment is necessary which corresponds to the pre-analysis.