Normal reference range of serum insulin-like growth factor (IGF)-I in healthy Thai adults.

BACKGROUND: Serum insulin-like growth factor (IGF)-I level is growth hormone (GH) dependent and reflects GH secretion. Analysis of IGF-I is a component in the diagnosis of GH-related disorders and is going to be of interest in determining the risk of many disorders such as cancer or atherosclerosis. The diagnosis value of IGF-I is dependent on the establishment of an accurate reference ranges, which can be affected by parameters such as age, gender, ethnicity, medications, chronic illness, or assay methodologies. OBJECTIVE: To determine reference ranges of IGF-I for healthy Thai adults. MATERIAL AND METHOD: Eight hundred sixteen healthy Thai adults aged between 21-70 years were recruited in the present study. Serum IGF-I was measured by using immunochemiluminescent (ICMA; Roche, USA). Subjects were recorded by their age and gender groups. Data were presented in mean and +/- 2 standard deviation (SD). Correlation analysis between serum IGF-I and physical parameters including sex, age, weight, height, and body mass index (BMI) was also made. RESULTS: The present study demonstrated normal reference range of serum IGF-I by using mean +/- 2 SD value. The well-known age dependency of serum IGF-I levels was also revealed. Levels decreased with increasing age in both genders. The mean value of serum IGF-I was slightly higher in women at the age of 30-40 years compared with men in the same age group, but not statistically insignificant. In addition, serum IGF-I was found to correlate directly with the height and negatively with BMI. However, age-adjusted IGF-I level did not show correlation with these physical parameters. CONCLUSION: This reference range will be beneficial for using IGF-I assay as a tool in the diagnosis of GH function abnormalities in Thai subjects.