Clearance rate of serum-free and total PSA following radical retropubic prostatectomy.

BACKGROUND

Our objective was to determine the clearance rate of free and total serum PSA following radical retropubic prostatectomy.

METHODS

Sera were obtained from 10 men with localized prostate cancer prior to and 1, 4, 8, 24, 48, and 72 hr after radical prostatectomy. No patient received any postoperative blood transfusion. Free and total PSA were measured using the Hybritech Tandem-R (total PSA) and radioimmunometric free PSA assay. Postsurgery serum-free and total PSA concentrations were modeled using a "two-compartment" pharmacokinetic model.

RESULTS

The pharmacokinetic model with an initial constant "infusion" suggests that, following release from the prostate, both free and total PSA are taken up into a second compartment for metabolism. The movement of PSA between these compartments was accurately modeled. Following surgery, there is a shift of both free and total PSA best modeled as a constant infusion into the serum at a rate of 1.97 and 1.60 ng/ml, respectively, for a period of approximately 1 hr. Following this initial constant infusion, the half-life estimations for free and total PSA are initially 1.2 and 0.75 hr, respectively, which then increase to 22 and 33 hr, respectively.

CONCLUSIONS

Serum free and total PSA are cleared from the circulation following a "two-compartment" model with an initial constant "infusion." The constant "infusion" is most likely a consequence of surgical manipulation. The initial half-life estimates are < 2 hr for both free and total PSA, and later increase to 22 and 33 hr, respectively.