CORRELATION OF SERUM CONCENTRATIONS OF PSA-ACT COMPLEX WITH TOTAL PSAIN RANDOM AND SERIAL SPECIMENS FROM PATIENTS WITH BPH AND PROSTATE-CANCER

The current assays for serum prostate specific antigen (PSA) have fail ed to produce the same PSA Values on the same specimens because of pro blems with antibody specificity and calibrator preparation. To elimina te these problems, we proposed to replace the current serum PSA assay with an assay specific for the PSA-ACT (PSA-alpha(1)-antichymotrypsin) complex in the serum. An assay specific for the PSA-ACT complex was e stablished using the anti-PSA antibody to coat the microplate for capt uring the PSA complex and anti-ACT polyclonal antibodies for quantific ation. There was an excellent correlation between serum concentrations of PSA-ACT and total PSA, using either the Hybritech calibrator (gamm a = 0.996) or a serum calibrator prepared in house (gamma = 0.993): in random as well as in serial specimens from 14 individual patients, Ev en though we did not find a gradual increase in the percentage of PSA- ACI with the increase of total PSA in cancer patients, a slightly high er percentage of free PSA was measured in pooled normal sera (18%) and in pooled sera containing only 12 ng/ml of total PSA (12%), compared to serum pools containing elevated PSA (>100 ng/ml) level, in which mo st PSA was in the complex form (95%). Therefore, using an assay that s pecifically measures the PSA-ACI complex in the serum not only simplif ies the preparation of calibrator but eliminates the difficulty of ant ibody selection. it also allows various assay kits to produce identica l PSA values and also improve the test specificity for prostate cancer . (C) 1995 Wiley-Liss, Inc.