A comparison of IGF-I levels measured by two commercially available radioimmunoassays.

Insulin-like growth factor I levels were measured in a parallel fashion in 77 extracted sera using the INCSTAR RIA (radioimmunoassay) and in the EDTA plasma of the same subjects by the NICHOLS RIA. The subjects suffered from untreated hGH deficiency, short stature, delayed and precocious puberty and acromegaly. Significant differences (P less than 0.05) were found between the mean IGF-I levels of all groups using both RIA systems. However, using the INCSTAR RIA, 85% of IGF-I values in untreated hGH deficiency were below normal, and a rise in IGF-I detected in the sera of all 5 patients who were treated with hGH. Using NICHOLS RIA, 55% of basal IGF-I values were below normal and a hGH-stimulated rise in IGF-I was found in only two of the treated patients. The INCSTAR RIA seems more precise and reproducible than the NICHOLS RIA and enables better discrimination of hGH-deficient patients from age-matched controls.