2023 Volume 72 Issue 4 Pages 549-556
Methods based on immunology are used to detect many hormones in sera. In these immunological methods, however, we occasionally find a discrepancy in the detection values between different reagents. The causes of such discrepancy include the influences of biotin or heterophil antibodies in patient serum on streptavidin, a common component of reagents. To determine the cause of the discrepancy, we examined differences of the FT3 levels by comparing three different reagents, namely, “former Elecsys FT3 III reagent” (former reagent) based on the electrochemiluminescence immunoassay (ECLIA), “improved Elecsys FT3 III reagent” (improved reagent) based on ECLIA, which is improved to prevent the negative effect on streptavidin, and “Accuraseed reagent” based on the chemiluminescent enzyme immunoassay (CLEIA). We observed a significant correlation between the FT3 levels of the former reagent and the improved reagent in 1,005 random serum samples. In contrast to the detection values of the former reagent, no unexpected elevation of the FT3 levels of the improved reagent with the addition of biotin into the serum was observed. We found a significant decrease in the FT3 level of the improved reagent in 13 out of 28 serum samples, which was observed with the dissociation between the FT3 levels of the former reagent and the improved reagent, and the existence of immunoglobulin was suspected in those 13 serum samples, as shown by the results of PEG, HBT, and Protein A analyses. Further studies are needed because it is still unclear why the FT3 levels of the improved reagent are different from those of the CLEIA in 15 out of 28 serum samples.
