[Study of non specific reactive phenomena in EIA method of CA 125].

We studied the false positive phenomena in immunoassay of CA 125 using mouse monoclonal antibody, and studied the natures of interfering substances. The serum CA 125 level in 405 patients was determined simultaneously by using the EIA and RIA methods. The overall correlation was good between CA 125 levels of the EIA and RIA methods. However, CA 125 levels in 41 cases were remarkably higher in the EIA method as compared with the RIA method. None of these patients had any disease that was known to result in elevation of the serum CA 125 level. The CA 125 activity of sera from five patients with remarkably discrepant values was contained in the column fractions corresponding to a molecular weight of human IgM in gel chromatography of TSK gel G 4000 SWXL that was smaller than the molecular weight of CA 125. To further determine whether IgM was involved in the CA 125 activity, we investigated the effect of adding anti-human IgM serum to discrepant sera. CA 125 activity was markedly reduced by the antiserum, whereas CA 125 activity in non-discrepant sera were not effected by this antiserum. Thus, data obtained from this group of experiments indicate that the interfering material in discrepant serum is IgM.