Growth failure with plasma GH that is normal by RIA but low by radioreceptor assay: responsiveness to exogenous GH.

We measured the ratio of GH by radioreceptor assay (RRA) using IM-9 cells to its radioimmunoassay (RIA) level in: (a) 25 children and young adults with normal growth (controls); (b) 7 poorly growing children with GH neurosecretory dysfunction (GHND) who had normal stimulated GH but subnormal integrated concentration of GH (IC-GH) who responded to GH therapy; (c) 4 poorly growing children who had both normal stimulated GH and IC-GH but did not respond to GH therapy (GHNR - GH responder), and (d) 7 poorly growing patients with normal stimulated, and IC-GH who responded to GH therapy (GHR - GH responder). The RRA/RIA ratio of the GHND group was 1.3 +/- 0.4 similar to that of the control group - 1.3 +/- 0.3. The mean RRA/RIA ratio of the 7 GHR patients was 0.6 +/- 0.5, significantly lower than the controls and the GHND patients (p < 0.05). The RRA/RIA ratios of the 4 GHNR patients was not different from the controls. We conclude that: (1) GH binding is normal in GHNR and GHND patients and (2) RRA/RIA ratio below the normal range as measured by IM-9 cell GH RRA in short, poorly growing children with normal GH secretion, was a predictor of the response to GH therapy.