Comparative study of serum human growth hormone measurement with NB2 lymphoma cell bioassay, IM-9 receptor modulation assay, and radioimmunoassay in children with disorders of growth.

The biological activity of GH in serum from 10 adult volunteers, 6 children with normal stature, and 26 children with growth retardation was assessed using the Nb2 rat lymphoma cell bioassay and the IM-9 human lymphocyte receptor modulation assay. The bioassay/RIA ratios for both bioassays varied widely but the range of ratios found in the normal stature adults and children was not different than that found in the group of children with growth retardation, which included 4 children with a presumptive diagnosis of bioinactive GH. We conclude that the use of these two bioassays is a valid approach to the assessment of the bioactivity of the circulating molecular forms of GH and that a large number of children with disorders of growth can be screened to identify patients with bioinactive GH.