Use of a two-site immunoradiometric assay for growth hormone (GH) in identifying children with GH-dependent growth failure.

Children with GH-dependent growth failure have normal GH responses to provocative stimuli, but, nonetheless, show increased growth rates when treated with replacement doses of human GH. We studied the GH secreted by 8 such children using a 2-site immunoradiometric assay for GH (IRMA-GH). To be detected in this assay, a GH molecule must be able to react simultaneously with two different monoclonal antibodies, each specific for a different region of the GH molecule. We compared the GH values observed in the IRMA to those obtained using classical RIA for GH (RIA-GH). The IRMA-GH to RIA-GH ratio was not affected by time of sample collection relative to peak GH serum levels in either normal individuals or children with GH-dependent growth failure. The ratios in serum samples from children with GH-dependent growth failure were significantly lower than those observed in normal individuals [0.35 +/- 0.005 vs. 0.48 +/- 0.02 (+/- SE); P less than 0.001]. All of the children with GH-dependent growth failure had IRMA-GH to RIA-GH ratios less than 0.4, while only 7 of 24 normal individuals had ratios this low (P less than 0.005). We suggest that a comparison of IRMA-GH with RIA-GH may supplement other clinical measurements and aid in identifying children with GH-dependent growth failure.