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Problems with growth hormone assays and strategies towards standardization

M Bidlingmaier, Neuroendocrinology, Ludwig Maximiliams University Munich, Munich, 80336, Germany

Correspondence: Martin Bidlingmaier, Email: martin.bidlingmaier{at}med.uni-muenchen.de

Abstract

Disorders affecting growth hormone secretion - either growth hormone deficiency or growth hormone excess (acromegaly) - are biochemically defined through peak or nadir concentrations of human growth hormone (GH) in response to dynamic tests. Immunoassays employing polyclonal or monoclonal antibodies are routinely used for the analysis of growth hormone concentrations, and many different assays are available on the market today. Unfortunately, the actual value reported for the GH concentration in a specific patient's sample to a large extent depends on the assay method used by the respective laboratory. Variability between assay results exceeds 200%, limiting the applicability of consensus guidelines in clinical practice. Reasons for the heterogeneity in GH assay results include the heterogeneity of the analyte itself, the availability of different reference preparations for calibration and the interference from matrix components such as GH binding protein. Furthermore, the reporting of results in mass units or international units together with the application of variable conversion factors led to confusion.

International collaborations proposed measures to improve the comparability of assay results, recommending the use of a single, recombinant calibrator for all assays and reporting only in mass units as first steps. However, because of the differences in epitope specificity of antibodies used in different assays, method specific cut-off levels for dynamic tests might remain necessary to correctly interpret and compare results from different laboratories.