Experimental determination of the operative parameters for a double antibody solid phase radioimmunoassay of luteinizing and follicle-stimulating hormones in serum

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Abstract
The experimental parameters of a Double Antibody Solid Phase (DASP) radioimmunoassay (RIA) for the determination of serum luteinizing (LH) and follicle-stimulating (FSH) hormones, are described. The lowest detection limits can be fixed at about 20 pg LH and about 10 pg FSH. Evidence of parallelism among the dose-response curves and the dilution curves of different sera is provided for FSH-RIA and for about 92 % of the tested sera for LH-RIA. The antisera dilution curves are reported (final titres: 1/160·103 for anti-LH and 1/40·103 for anti-FSH). The traditional cross-reaction study in buffer indicates that 5.38 and 46.81 µU TSH/ml mimic 1 ng LH/ml and 1 ng FSH/ml respectively. The regression-line equations of antigen recovery (f=found, e=expected) are: LH f=0.94 LH e+0.91 and FSH f=1.05 FSH e+0.17; the same equations when TSH is added become: LH f=1.30 LH e+1.46 and FSH f=1.40 FSH e—0.37. It is concluded that LH-RIA is interfered by TSH over 8–10 µU TSH/ml and in function of TSH concentration; FSH-RIA is not interfered by TSH up to 4–5 ng FSH/ml; for higher FSH levels, TSH interferes according to a linear law (angular coefficient 1.40) and not in function of its concentration. LH and FSH levels throughout normal menstrual cycle in follicular phase, centre peak and luteal phase are: 3.14±1.16, 16.71±12.99, 2.31±1.04 ng LH/ml (mean±2SD) and 3.57±0.95, 5.72±2.90, 2.57±0.80 ng FSH/ml (mean±2SD) respectively. Finally, the within-assay coefficient of variation is 7.65 % for LH-RIA and 3.16 % for FSH-RIA.