Age- and sex-specific reference values for fasting serum insulin levels and insulin resistance/sensitivity indices in healthy Iranian adults: Tehran Lipid and Glucose Study

Objectives: Increased insulin concentration is a surrogate for insulin resistance and early assessment of fasting insulin may help in identifying those who are potentially at high risk of type 2 diabetes, hypertension, and cardiovascular disease. The aim of this study was to determine age-and sex-related reference values for serum insulin and insulin resistance/sensitivity indices in Iranian subjects. Design and methods: Serum insulin levels were measured by electrochemiluminescence immunoassay in 5786 participants of the Tehran Lipid and Glucose Study. After application of exclusion criteria, 309 non-obese healthy subjects (124 men and 185 women), aged 24-83 y, were included. The International Federation of Clinical Chemistry guidelines (non-parametric method) and the robust method were used for determining reference values. Results: Overall 95% reference values for fasting insulin were 1.61-11.37, 2.34-11.98, and 2.11-12.49 mu U/mL in men, women, and total population respectively. Mean fasting insulin concentration showed a decreasing trend with age in both genders (p for trend <= 0.001). Age, waist circumference, and systolic blood pressures were biological determinants of fasting insulin in both genders; in addition, insulin was modulated by triglycerides in men and fasting glucose in women. Reference intervals for HOMA1-IR, HOMA2-IR, and QUICKI were 0.63-2.68, 0.40-1.80, and 0.33-0.42, respectively. Conclusion: This study presents the first set of reference values for fasting serum insulin to be 2-12 mu U/mL for both genders in a healthy sample of Iranian adults along with the reference values for insulin resistance/sensitivity indices. These values could be used for identifying subjects with insulin resistance in epidemiological and clinical research. (C) 2014 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.