Radioimmunoassays of human luteinizing and follicle-stimulating hormones using the same radioactive tracer.

The National Institute of Diabetes, Digestive and Kidney Diseases (NIDDK) provides the hFSH-I-3 preparation, to be employed as a tracer in the radioimmunoassay (RIA) of human follicle-stimulating hormone (hFSH). The contaminating LH contained in that preparation led us to study whether the iodination of such a material could render it a suitable tracer for RIA of both LH and FSH. hFSH-I-3 was labelled with 125I by the chloramine-T method and was further purified on Sephadex G-75 column. The LH-RIA was performed using this preparation and anti-LH at a final dilution of 1:37,500, with a sensitivity of 3 mIU LH/ml (2nd international reference pattern). The method was validated by comparing the LH values obtained in different serum samples with those obtained using the standard RIA (125I-LH/anti-LH); the correlation coefficient (r) was equal to 0.9988. No LH overestimation due to the putative cross-reaction with FSH was found. This was demonstrated by testing serum samples containing high (greater than 100 mIU/ml) and low (less than 10 mIU/ml) concentrations of FSH before and after the treatment with anti-LH. Under these conditions, serum samples from postmenopausal women, pregnant women, normal men and women in basal conditions and after the LH-RH administration, and from a patient with Klinefelter's syndrome, were evaluated. In conclusion, NIDDK 125I-hFSH-I-3 can be used as a tracer for the radioimmunological quantitation of both hLH and hFSH, which results not only inexpensive, but also allows to reduce the amount of the stored radioactive materials.