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.


METHODS
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.


CONCLUSIONS
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.
Friedrich
Nele
N
Institute for Community Medicine, Ernst Moritz Arndt University, Walther-Rathenau-Strasse 48, D-17487 Greifswald, Germany. nele.friedrich@uni-greifswald.de
Alte
Dietrich
D
Völzke
Henry
H
Spilcke-Liss
Elisabeth
E
Lüdemann
Jan
J
Lerch
Markus M
MM
Kohlmann
Thomas
T
Nauck
Matthias
M
Wallaschofski
Henri
H
D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood; D005260:Female; D005858:Germany; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012044:Regression Analysis; D012727:Sex Characteristics
D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I