Characteristics and reference ranges of Insulin-Like Growth Factor-I measured with a commercially available immunoassay in 724 healthy adult Caucasians

Abstract

Background and Objective: Measurements of Insulin-Like Growth Factor-I (IGF-I) play a pivotal role in the evaluation of the growth hormone-IGF-I axis. Due to assay variation IGF-I reference ranges are assay specific. We provide serum IGF-I reference ranges for adult men and women obtained by a commercially available assay. Method: IGF-I was measured by an enzyme-linked immunosorbent assay (R&D Systems). Assay precision was evaluated in low, medium and high IGF-I pools and in single samples from outpatients. The reference ranges were obtained in 724 healthy Caucasians, mean age 48 years (range 19–91). Results: IGF-I was measured higher in serum compared to plasma samples (p<0.001, R²=0.96). To convert EDTA plasma values to serum values a factor of 1.22 was calculated. The intraassay coefficients of variation (CV) for the low: 56.4±2.7ng/mL, medium: 179.7±5.9ng/mL and high pool: 445.61±3.2ng/mL (mean 1SD) were 5, 3 and 3%. Interassays CVs for the low, medium and high pool varied between 7–10, 5–7, and 6–9%. Reproducibility between 4 different lots showed a intraclass CV of 0.99 (95%CI 0.98–0.96). Logarithmically transformed IGF-I levels were linearly associated with age with a 13% reduction in IGF-I per decade in females and 11% in males. Conclusion: We have provided IGF-I reference ranges obtained by an assay that showed variations and reproducibility that was considered of sufficient high quality for clinical and scientific use.

Key Words::

• Growth hormone
• Insulin-like growth factor 1
• reference ranges
• assay validation
• Enzyme-Linked Immunosorbent Assay

Acknowledgements

We thank Ulla Kjerulff-Hansen, Tonni Løve Hansen, and Debbie Nadelmann for the measurement of IGF-I and Tobias Wirenfeldt Klausen for statistical support, all from Herlev Hospital.

We thank Dr Per Hildebrandt from the Department of Cardiology at Glostrup Hospital, Denmark for access to data from the Frederiksberg Heart Failure Study.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.