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Assay‐Dependent Results of Immunoassayable Spontaneous 24‐Hour Growth Hormone Secretion in Short Children

ABSTRACT. Forty‐eight children, referred for evaluation of short stature, underwent 24‐hour spontaneous growth hormone (GH) secretion studies. The GH level in pooled sera was assessed for each child, using up to 11 commercial immunoassays. In a group of 15 children, the mean GH values obtained by nine of the assays were compared with the mean value given by a polyclonal radioimmunoassay (RIA) from Sorin: four gave higher results (p < 0.0001), three gave comparable results and two gave lower results (p < 0.001). The assay yielding the highest results (Nichols: 5.9 ± 2.3 ng/ml, mean ± SD) gave values that were approximately triple those obtained by the assay yielding the lowest results (Hybritech: 1.8 ± 0.8 ng/ml; p < 0.0001); both of these are monoclonal immunoradiometric assays (IRMAs). The GH concentrations measured in 24‐hour pools from 32 children using a monoclonal IRMA from Biomerieux were similar to those obtained using a polyclonal RIA from Farmos (2.8 ± 1.1 ng/ml and 2.9 ± 1.4 ng/ml, respectively) but significantly lower than those measured by another polyclonal RIA from Sorin (3.5 ±1.5 ng/ml). Two polyclonal assays (Biomérieux and Sorin) were then used to measure the GH levels in all of the 30‐minute samples and in the day, night and 24‐hour pools from the secretion studies of 22 children. The ratio of the results of the two assays remained fairly constant for a given child (although the GH levels in different 30‐minute samples differed considerably). However, the ratios between different children showed quite wide variation (from 2.03 to 1.04). It was concluded that the GH assay must be taken into account when evaluating data from GH secretion studies, and the disparity in the GH level measured by two or more assays may differ from child to child.