Objectives: The aim of this study was to investigate whether a significant difference consists between patients with and without prostate carcinoma (CaP) regarding the ratio of prostate-specific antigen (PSA) in complex with major proteinase inhibitors to noncomplexed (free) PSA (FPSA).
Methods: We analyzed the sera of 29 patients with untreated CaP, 34 patients with benign prostatic hyperplasia (BPH), and 33 men with no symptoms of prostate disease for the amount of FPSA and total PSA (TPSA) with the Immulite chemiluminescent enzyme immunometric assay.
Results: FPSA was found only as a minor fraction in all sera tested. Calculation of the percentage of FPSA from TPSA revealed a significant difference between patients with CaP (median, 9.55%) versus patients with BPH (median, 17.07%; P = 0.00001) or versus healthy men (median, 16.11%; P = 0.0006). Considering only patients with PSA values less than 10 ng/mL, the difference between patients with CaP versus patients with BPH remained significant (P = 0.026). The specificity for differentiation between CaP and BPH at a sensitivity level of 89% for the combined evaluation of the proportion of FPSA and TPSA increased from 30% (TPSA considered alone) to 61%. The cutoff level for TPSA was determined at 4 ng/mL and for the proportion of FPSA at 21.1%.
Conclusions: These data indicate that the differentiation between CaP and BPH can be considerably improved by measuring both FPSA and TPSA and calculating the ratio of the one to the other.