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The Proportion of Prostate-specific Antigen (PSA) Complexed to ₁-Antichymotrypsin Improves the Discrimination between Prostate Cancer and Benign Prostatic Hyperplasia in Men with a Total PSA of 10 to 30 µg/L

¹ Department of Urology,
² Research Center, and
³ Department of Clinical Pathology, La Fe University Hospital, 46009 Valencia, Spain.

^aAddress correspondence to this author at: Hospital Universitario La Fe, Centro de Investigación, Avda. Campanar 21, 46009 Valencia, Spain. Fax 34-96-3868718; e-mail espanya_fra{at}gva.es.

Background: The aim of this study was to assess the diagnostic accuracy of the proportion of prostate-specific antigen (PSA) complexed to ₁-antichymotrypsin (PSA-₁ACT:PSA ratio) in the differential diagnosis of prostate cancer (CaP) and benign prostatic hyperplasia (BPH) in men with total PSA of 10–30 µg/L.

Methods: We used our immunoassays (ELISAs) for total PSA and PSA-₁ACT complex to study 146 men. In 123, total PSA was between 10 and 20 µg/L; 66 of these had CaP and 57 BPH. In 23 men, total PSA was between 20 and 30 µg/L; 14 of these had CaP and 9 BPH. We calculated the area under the ROC curves (AUC) for total PSA, PSA-₁ACT complex, and PSA-₁ACT:PSA ratio, and determined the cutoff points that gave sensitivities approaching 100%.

Results: In the total PSA range between 10 and 20 µg/L, the AUC was significantly higher for the PSA-₁ACT:PSA ratio (0.850) than for total PSA (0.507) and PSA-₁ACT complex (0.710; P <0.0001). A cutoff ratio of 0.62 would have permitted diagnosis of all 66 patients with CaP (100% sensitivity) and avoided 19% of unnecessary biopsies (11 of 57 patients). In the total PSA range between 20 and 30 µg/L, the AUC for the PSA-₁ACT:PSA ratio (0.980; 95% confidence interval, 0.82–0.99) was greater than the AUC for total PSA (0.750; 95% confidence interval, 0.51–0.89; P = 0.042). In this range, a cutoff point of 0.64 would have permitted the correct diagnosis of all 14 patients with CaP and 6 of the 9 with BPH.

Conclusions: The diagnostic accuracy of the PSA-₁ACT:PSA ratio persists at high total PSA concentrations, increasing the specificity of total PSA. Prospective studies with large numbers of patients are needed to assess whether the ratio of PSA-₁ACT to total PSA is a useful tool to avoid unnecessary prostatic biopsy in patients with a total PSA >10 µg/L.

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