DIFFERENCES IN SERUM LUTEINIZING-HORMONE MEASUREMENTS BY IMMUNORADIOMETRIC ASSAY INDUCED BY KINETIC MANIPULATION OF ASSAY CONDITIONS ARE DEPENDENT ON THE ENDOCRINE MILIEU OF SERUM

Divergent estimates for luteinizing hormone (LH) in individual serum s amples may be given by different immunoassays. In order to investigate this phenomenom further, we have studied the effect of differences in assay kinetics within the same immunoradiometric assay (IRMA) configu ration on LH measurement in sera from different endocrine states. Thre e pairs of monoclonal/polyclonal two-site IRMA systems for LH were dev eloped from three LH monoclonal antibodies and a common polyclonal ant ihuman chorionic gonadotrophin. For IRMA systems a short and long assa y, which were different only with respect to the incubation time (1/2h and overnight respectively), of the labelled monoclonal first antibod y were performed. The IRMAs were all standardized against the LH inter national reference preparation 68/40. LH concentrations were measured by all the IRMAs in sera obtained from normal men (n = 11) and from wo men with polycystic ovarian syndrome (PCO; n = 13). In normal men, the re were no differences in LH estimates between the short and the long assays of the three IRMA systems, and the ratios of long to short assa ys were similar for all the systems. However, in PCO there were signif icant differences between short and long assays and the ratios of long to short assays were different for the IRMA systems. These results in dicate that kinetic differences between IRMAs of the same antibody con figuration can be associated with differences in measured LH concentra tions, depending on the endocrine status of the sera studied. As LH gl ycoform patterns are known to differ between normal men and PCO, the o bserved changes in LH estimates may be due to the different glycoform composition.