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Free and complexed prostate specific antigen in the differentiation of benign prostatic hyperplasia and prostate
1Department of Urology, La Fe University Hospital, Valencia, Spain.
Purpose:
We prospectively evaluated serum and plasma concentrations of total and free prostate specific antigen (PSA), and PSA complexed to alpha1-antichymotrypsin in 170 patients who underwent biopsy, including 59 with prostate cancer and 111 with benign prostatic hyperplasia. We compared the usefulness of the ratios of free-to-total and complexed-to-total PSA for distinguishing between prostate cancer and benign prostatic hyperplasia, and studied the influence of blood clotting on the ratios.
Materials And Methods:
Blood samples were processed to generate serum and citrated plasma. To calculate complexed-to-total and free-to-total PSA we assayed plasma and serum samples for total and complexed PSA using homemade immunoassays, and total and free PSA using the Immulite assay. The 2 total PSA assays were compared using the Tandem-E PSA assay. Receiver operating characteristics curves were constructed for the total population, and for 2 to 20, 4 to 20, 2 to 10 and 4 to 10 ng./ml. total PSA.
Results:
In all groups complexed-to-total PSA had higher specificity than free-to-total and total PSA, especially at 90 to 100% sensitivity. Generally citrated plasma samples provided higher specificity than serum samples for all sensitivity values. The best performance for complexed-to-total and free-to-total PSA was obtained in the subset of patients in whom total PSA was 2 to 10 ng./ml.
Conclusions:
Our results indicate that the complexed-to-total PSA ratio performed better for classifying disease status than the free-to-total PSA ratio in the whole patient population and in the diagnostic gray zone of 2 to 10 ng./ml. In addition, plasma samples should be used to calculate the complexed-to-total and free-to-total PSA ratio.