Reference ranges of serum IGF-1 and IGFBP-3 levels in a general adult population:: Results of the Study of Health in Pomerania (SHIP)

Objective: Insulin-like growth factor I (IGF-1), which is mostly carried by IGF binding protein 3 (IGFBP-3), mediates endocrine actions of growth hormone and represents an important prognostic factor for systemic diseases. The main objectives of the present study were (1) to calculate age- and sex-specific reference values for serum IGF-1 and IGFBP-3 levels using the Gaussian mean +/- 1.96 * standard deviation method and the quantile regression method and (2) to perform a comparison of the results from both statistical methods. Design: Cross-sectional study (Study of Health in Pomerania). The study population included 2499 men and women aged 20-79 years. Methods: Serum IGF-1 and IGFBP-3 levels were determined by chemiluminescence immunoassays. Linear and quantile regressions were performed to calculate age- and sex-related reference ranges. Results: Both statistical methods generated different results: The reference ranges based on linear regression identified 43 (1.7%) subjects with serum IGF-1 levels and 99 (4.0%) subjects with serum IGFBP-3 levels outside the reference range. Using quantile regression, 117 (4.7%) or 118 subjects (4.7%) with serum IGF-1 or IGFBP-3 levels outside the range were detected, respectively. Conclusion: The present study established age- and sex-specific reference ranges for serum IGF-1 and IGFBP-3 levels. Quantile regression should be preferred to calculate reference ranges because a better concordance to original data is possible due to no distribution assumption are required and the robustness against outliers is given. (c) 2007 Elsevier Ltd. All rights reserved.