ULTRA-SENSITIVE ASSAY OF GROWTH HORMONE IN SERUM

Abstract

In the last few years the immunological methods for measurement of serum GH have been subject to criticism because of discordance between results obtained from different laboratories and poor sensitivity of most assay systems. Aim of our study was to develop an ultra-sensitive assay for GH and to evaluate its utility for the assessment of the GH secretory status. For this purpose we adapted an ELISA-test for the measurement of GH in urine to the measurement of serum GH. Due to the high concentration of serum GH versus urinary GH, a dilution of the serum samples was required. The assay is performed in microtiler plates coated with a monoclonal GH antibody. Sample size is 100μ1 serum diluted 1:100 or 1:400. The assay is completed within 24 hours. The characteristics of this ultra-sensitive GH assay are as follows: minimum detectable concentration: 0.514 ng/L; intraassay coefficients of variation: 10.9% (1.80 ng/L) and 4.4% (9.74 ng/L); interassay coefficients of variation: 17.5% and 13.8% at the same concentrations. Serial dilutions of serum samples were linear and parallel to the standard curve. For the latter r-hGH was used. To assess the utility of the assay, we measured a) samples from 24 hour studies in healthy adult volunteers; b) samples drawn before and after stimulation of GH in children operated for craniopharyngioma. A concentration of GH could be measured in every single serum sample, the lowest found so far being 0.97 ng/L, a value which is statistically different from the minimum detectable concentration for the assay. This ultra-sensitive assay for GH should open new perspectives for the investigation of GH secretion.