CLEARANCE OF PSA AFTER RADICAL PROSTATECT OMY - A SUITABLE MODEL FOR CALCULATION OF PSA HALF-LIFE

A review of the literature relating to PSA half-life reveals great var iability in absolute values and pharmacokinetic models. A critical vie w is needed, however, since some authors suggest that the PSA half-lif e has implications for diagnosis and prognosis after radical prostatec tomy, The aim of our study, therefore, was to characterize the value o f PSA half-life determination after radical prostatectomy. Serial seru m PSA detections were performed in 16 patients with localized prostati c cancer who had undergone radical prostatectomy. Serum PSA was detect ed on days 0, 1, 2, 3, 6, 9, 12, 15, 18 after radical prostatectomy. I n all patients elimination of PSA from serum followed a biphasic logar ithmic decay pattern indicating a two-compartment model of first order elimination kinetics (t(1) = 1.01 +/- 0.06 days, t(2) = 3.32 +/- 0.23 days; P < 0.00001), In this two-compartment model 56.3 +/- 4.8% of th e preoperative PSA serum concentration was cleared by the first compar tment. To find a biological correlative for the first compartment a ma thematical model was developed to approximate the effect of operative blood and plasma loss on PSA serum concentration, In this model change s of hematocrit were used to estimate blood and plasma loss. These cal culations showed that 50.12 +/- 3.04% of the preoperative PSA serum co ncentration was excreted by operative blood loss. This value was not s ignificantly different from the clearance rate calculated for the firs t compartment, It is, therefore, concluded that the determination of P SA half-life after radical prostatectomy without correction of the ope ration-related PSA loss is only of limited value.