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

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.

To determine reference ranges of IGF-I for healthy Thai adults.

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.

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.

This reference range will be beneficial for using IGF-I assay as a tool in the diagnosis of GH function abnormalities in Thai subjects.