Assay of follitropin and lutropin by fluorescence enzyme immunoassay

Recently developed fluorescent enzyme immunoassays (FEIs) for follitropin (FSH) and lutropin (LH) designed for the Stratus analyzer were compared with a typical dual FSH-LH radioimmunoassay (RIA) procedure. The FEIs use monoclonal antibodies in a sandwich reaction scheme similar to that of immunoradiometric procedures but with filter paper tabs rather than polystyrene beads and alkaline phosphatase as a tag instead of a radioisotope. Precision of the FEI was comparable with that of the RIA tests with CVs typically under 10%. The detection limit of the FSH test is 0.4 IU/L and that of the LH test is 0.6 IU/L. Measurable carryover exists but is clinically inconsequential. Neither assay exhibits total specificity, but the degree of cross-reactivity is unlikely to be problematic in most situations. Recovery with the FSH assay was 103%, with the LH assay, it averaged 108%. Moderate amounts of bilirubin and triglycerides and gross hemolysis caused no significant interferences. Method comparison studies yielded the following: FEI for FSH, 1.16 RIA + 3.1, r = 0.97, n = 114; FEI for LH, 0.77 RIA - 0.23, r = 0.96, n = 112. Difference analysis of the method comparison data revealed relatively poor agreement between the FEI tests and the dual RIA procedure. With the adoption of method-specific normal reference ranges, the FEI tests offer attractive alternatives to radioisotopic FSH and LH assays.