Differences in the Distribution of IGF-I Concentrations Between European and US Populations

Area of Science:

• Endocrinology
• Clinical Chemistry
• Biomarker Analysis

Background:

• Method-specific reference intervals (RIs) are crucial for interpreting Insulin-like Growth Factor I (IGF-I) levels in growth hormone (GH)-related diseases.
• Population-specific variations can impact the clinical utility of established RIs.

Purpose of the Study:

• To compare population-specific RIs for IGF-I derived from routine laboratory testing in the United States and Europe.
• To assess the applicability of RIs across different geographical regions and demographic groups.

Main Methods:

• Utilized uncensored routine IGF-I testing data from four accredited laboratories (US and Europe) over five years.
• Constructed RIs using the indirect statistical modified Hoffmann approach.
• Compared derived RIs with published data and between US regions with differing mean body mass indexes (BMIs).

Main Results:

• Lower limits (LLs) of RIs were comparable between US and European datasets and with published RIs.
• Upper limits (ULs) derived from US routine data were significantly higher than those from European data for both children and adults.
• IGF-I levels were higher in samples from a lower BMI region in the US compared to a higher BMI region, but differences were smaller than US-Europe comparisons.

Conclusions:

• The indirect Hoffmann approach yields comparable RIs to direct sampling in large datasets.
• Significant differences exist in IGF-I upper limits between the United States and Europe.
• Adapted RIs for the United States are recommended to ensure accurate clinical interpretation.