Validation of Functional Insulin-Like Growth Factor Binding Protein-3 Measurement by a Ligand Immunoassay

Langkamp, M.; Weber, K.; Kirschner, M.; Pridzun, L.; M.B. Ranke

Clinical Laboratory 56(11-12): 535-542

2010


ISSN/ISBN: 1433-6510
PMID: 21141437
Document Number: 15991
Background: Proteolysis of Insulin-like Growth Factor Binding Protein (IGFBP) – 3 is a well known mechanism regulating IGF-I bioavailability and IGF-independent actions of IGFBP-3 fragments. Measurement of functional IGFBP-3 can be of use in diagnostics of growth failure or renal impairment. We herein characterize the properties of a commercially available immunoassay for the measurement of functional (IGF-I binding) IGFBP-3. Method: Fragmentation of IGFBP-3 is analyzed by gel filtration, SDS-PAGE, and western ligand and immunoblotting and compared with subsequent measurement of total and functional IGFBP-3 by ELISA/IFA. Furthermore, assay characteristics such as reproducibility, linearity, and sensitivity are surveyed. Results: Functional IGFBP-3 was reproducibly measured (6.8/5.6 % Inter-/Intra assay variance). A broad range of linearity (1:50 – 1:300) and a high sensitivity (0.18 µg/L) allowed reliable measurement of IGF-binding IGFBP- 3. Analysis of IGFBP-3 fragments reveals that the assay described only detects intact IGFBP-3. Analysis of 189 serum samples from healthy blood donors showed that on average 84 % and 69 % of total IGFBP-3 was functional in men and women, respectively (p Conclusions: Functional IGFBP-3 can be measured reliably by the assay system used. Thus, this assay system is suited for the investigation of the diagnostic value of functional IGFBP-3 in human body fluids.

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Validation of Functional Insulin-Like Growth Factor Binding Protein-3 Measurement by a Ligand Immunoassay