Growth Hormone Assessment by Radioreceptor and Radioimmunoassay: Radioreceptor Assay and Radioimmunoassay Comparisons

To investigate possible human growth hormone (HGH) bioinactivity, serum radioreceptor assay (RRA) and radioimmunoassay (RIA) comparisons were made in 48 children undergoing an evaluation for growth retardation. Discrepancies between serum HGH concentrations by RRA and RIA were uncommon; the overall RRA/RIA ratio was 0.75. Significantly reduced HGH RRA/RIA ratios were seen at peak time periods following levodopa and arginine hydrochloride stimulation. Two subjects who demonstrated a discrepancy between serum HGH concentrations by RRA and RIA and somatomedin C levels in the hypopituitary range had malnutrition and chronic disease. There appeared to be an inverse correlation between nutrition, as assessed by a height age—weight age ratio, and RRA/RIA ratios in all subjects. While a reduced RRA/RIA ratio supports the diagnosis of bioinactive HGH, the administration of certain HGH secretagogues, malnutrition, and chronic disease may result in low HGH RRA/RIA ratios.