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Problems with GH assays and strategies toward standardization.
1Endocrine Research Laboratories, Medizinische Klinik, Innenstadt, Ludwig-Maximilians University, Ziemssenstreet 1, 80336 Munich, Germany. martin.bidlingmaier@med.uni-muenchen.de
European Journal of Endocrinology
|September 30, 2008
Summary
Assays for human growth hormone (GH) show over 200% variability, complicating diagnosis of GH deficiency and acromegaly. Standardizing calibration and reporting is needed, but method-specific cut-offs may persist.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Biochemical Assays
Background:
- Growth hormone (GH) disorders, including deficiency and excess (acromegaly), are diagnosed using dynamic tests measuring GH concentrations.
- Immunoassays with polyclonal or monoclonal antibodies are standard for GH analysis, but numerous commercial assays exist.
Purpose of the Study:
- To highlight the significant variability in human GH assay results.
- To discuss the implications of this variability for clinical practice and diagnostic guidelines.
Main Methods:
- Analysis of existing literature and data on human GH immunoassays.
- Discussion of factors contributing to assay heterogeneity, including analyte properties, calibration standards, and matrix interferences.
Main Results:
- Assay results for GH concentration can vary by over 200%, significantly limiting the clinical applicability of consensus guidelines.
- Heterogeneity stems from the GH analyte itself, diverse calibration preparations, and matrix components like GH-binding protein.
- Inconsistent reporting units (mass vs. international units) and conversion factors add to confusion.
Conclusions:
- International efforts propose using a single recombinant calibrator and mass units to improve assay comparability.
- Despite standardization measures, differences in antibody epitope specificity may necessitate method-specific cut-off levels for accurate interpretation of dynamic GH tests.
