[Is radical prostatectomy a suitable model for determination of PSA half-life?]

A review of the literature relating to PSA half-life reveals great variability in absolute values and pharmacokinetic models. A critical view is needed, however, since some authors suggest that the PSA half-life has implications for diagnosis and prognosis after radical prostatectomy. The aim of our study, therefore, was to characterize the value of PSA half-life determination after radical prostatectomy. Serial serum PSA detections were performed in 16 patients with localized prostatic cancer who had undergone radical prostatectomy. Serum PSA was detected on days 0, 1, 2, 3, 6, 9, 12, 15, 18, after radical prostatectomy. In all patients elimination of PSA from serum followed a biphasic logarithmic decay pattern indicating a two-compartment model of first order elimination kinetics (t1 = 1.01 +/- 0.06 days, t2 = 3.42 +/- 0.23 days; P < 0.00001). In this two-compartment model 56.3 +/- 4.8% of the preoperative PSA serum concentration was cleared by the first compartment. To find a biological correlative for the first compartment a mathematical model was developed to approximate the effect of operative blood and plasma loss on PSA serum concentration. In this model changes of hematocrit were used to estimate blood and plasma loss. These calculations showed that 50.12 +/- 3.04% of the preoperative PSA serum concentration was excreted by operative blood loss. This value was not significantly different from the clearance rate calculated for the first compartment. It is, therefore, concluded that the determination of PSA half-life after radical prostatectomy without correction of the operation-related PSA loss is only of limited value.