Ratios of free to total prostate-specific antigen (f/t PSA ratio) improved differentiation of benign prostatic hyperplasia (BPH) from prostate cancer (CaP). Using sera obtained at least 1 month prior to biopsyconfirmed diagnosis and logistic regression adjusted for disease prevalence, probability curves are constructed to predict the presence of CaP.

The patient population included 122 (44%) BPH sera and 155 (56%) prostate carcinoma sera collected prior to any therapy. The total PSA range = 2.0–20.0 ng/mL; median age = 69 years. External reference standards for both free and total PSA assays were used to standardize the assays and correct the ratio. Probability curves and tables for cancer incidence were formulated for a subset of the total test population (total PSA range = 2.0–10.0 ng/mL; 98 BPH, 118 CaP patients) by using logistic regression and prior cancer prevalence statistics derived from a published patient screening study.

Median f/t PSA ratios were 0.18 and 0.12 in the overall sample and 0.19 and 0.12 in the subset for BPH and CaP, respectively (P = 0.0001). The median total PSA concentrations for BPH and CaP were 5.8 and 6.7 ng/mL when total PSA range = 2.0–20.0 ng/mL and were 4.9 and 5.9 ng/mL when total PSA range = 2.0–10.0, respectively.

Cancer probability curves were constructed to help guide decisions concerning biopsy and other aspects of prostate cancer disease management. Further validation of this approach in another series of patients is necessary and is planned.