DUAL-LABEL ONE-STEP IMMUNOASSAY FOR SIMULTANEOUS MEASUREMENT OF FREE AND TOTAL PROSTATE-SPECIFIC ANTIGEN CONCENTRATIONS AND RATIOS IN SERUM

We developed a simple one-step dual-label immunoassay for simultaneous measurement of the free, noncomplexed form of prostate-specific antig en (PSA) and total PSA. The assay is based on time-resolved fluorescen ce and includes a stable fluorescent chelate of Eu to label a monoclon al antibody (mAb) that detects only free PSA, whereas a second mAb lab eled with a fluorescent chelate of Tb provides equimolar detection of both free PSA and PSA complexed to alpha(1)-antichymotrypsin. A third mAb on a solid phase captures the free and complexed forms of PSA in a n equimolar fashion. The simultaneous measurement of the free-to-total PSA ratio (F/T) with the one-step dual assay is not sensitive to vari ations in the sample volume. The discrimination between benign prostat ic hyperplasia and prostate cancer patients, i.e., the area under the receiver-operating characteristic curve, increased from 0.64 (total PS A assay) to 0.78 and 0.81 when the F/T ratio was measured with single and dual assays, respectively.