Insulin-like growth factor 1 (IGF-1, Somatomedin C) Blood Test

Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a hormone similar in molecular structure to insulin which plays an important role in childhood growth, and has anabolic effects in adults.

The median serum IGF-I level was 374.1 ng/ml at the age of 18. The serum IGF-I level decreased to 180.1 ng/ml at the age of 35–39, which is 48.1% of that at age 18, and further decreased to 92.7 ng/ml at ages older than 70, which is approximately 24.8% of that at age 18.

If the IGF-1 level is decreased, then it is likely that there is a growth hormone (GH) deficiency or an insensitivity to GH. If this is in a child, the GH deficiency may have already caused short stature and delayed development and may be treated with GH supplementation. Adults will have an age-related decrease in production, but lower than expected levels may reflect a GH deficiency or insensitivity.

Possible causes of elevated IGF-1 levels include: acromegaly (especially when GH is also high), high-protein diet, high glycemic-index diet, dairy products (except for cheese) consumption, delayed puberty, pregnancy, hyperthyroidism, IGF-1 assay problems, some rare tumors (i.e. carcinoids).