RESUMEN
OBJECTIVE: Since its discovery as a marker for prostate cancer, there have been many attempts to enhance the diagnostic efficacy of the prostate specific antigen (PSA). Among these are the studies that analyze the behavior of different forms of serum PSA bound to different antiproteases, such as alpha-1-antichymotrypsin, which forms the complexed PSA (PSA-c). This study analyzed the utility of PSA-c to enhance specificity without altering sensitivity in comparison to total PSA (PSA-t). METHODS: From September 1998 to March 1999, blood samples were obtained from 96 patients that had undergone a prostate biopsy due to a suspicion of prostate cancer. PSA-c, PSA-t (Technicon Immunol system, Bayer) and PSA-c/PSA-t ratio were analyzed in these patients. RESULTS: ROC curves were plotted and the optimal cutoffs were found for which the specificity was higher for PSA-c (44.6% [CI 95%, 32-57]) versus PSA-t (35.4% [CI 95%, 25-49]) and the PSA-c/PSA-t ratio (38.5% [CI 95%, 27-51]) while maintaining a similar sensitivity index (90%). PSA-c showed similar results for other values of sensitivity. CONCLUSIONS: PSA-c was found to improve specificity in comparison to PSA-t and PSA-c/PSA-t ratio. PSA-c determination could avoid unnecessary biopsies without altering sensitivity; i.e., the same number of prostate cancers will be detected.