Discordances entre les dosages de PSA : comparaison PSA, PSA libre, PSA complexé

Abstract

Prostatic Specific Antigen (PSA) associated with digital rectal examination is proven to be a powerful tool in the early detection of prostatic carcinoma. The discrepancy of the results between the different methods leads to less accurate clinical diagnosis. The existence of several molecular forms of circulating PSA generate these discrepancies in total PSA determination (TPSA). The structure of immunoassay explains the differences in immunologic recognition and amounts of circulating PSA. Reliability can be obtained by accurate standardizations which reduce intertest variability, but do not increase intrinsic clinical performance of total PSA. The determinations of free (FPSA) or complexed (CPSA) PSA and more precisely the FPSA/TPSA or CPSA/TPSA ratios, seem to give more accurate and more specific answer than total PSA alone for the early diagnosis and therapeutic follow-up of prostatic carcinoma. The study of 456 patients from the Urologic Surgery Ward of Cochin Hospital including 195 patients with benign prostatic hypertrophy (BPH), 138 pa-tients with prostatic carcinoma (PC) and 123 patients without PC provides optimal threshold values for the FPSA/TPSA ratio (ratio - 18% with sensitivity = 70% and specificity = 90%). ROC analysis shows that CPSA/TPSA ratio gives the same clinical performances as FPSA/TPSA ratio.