Human Growth Hormone Test

What is IGF-1?

IGF-1, also known as Somatomedin C, is a polypeptide hormone similar in structure to insulin and primarily produced in the liver. It is one of the main mediators of the actions of growth hormone in promoting muscular and skeletal growth. IGF-1 is itself a powerful anabolic hormone, and it also prevents premature cell death by inhibiting apoptosis. Because of its similarity to insulin, it also weakly activates the insulin receptor and therefore has insulin-like effects when present in large quantities. These binding proteins stabilize IGF-1, prolonging its half-life in the bloodstream.  IGF-1 is stable in whole blood dried on filter paper and therefore can be conveniently and accurately measured in dried blood spots1. IGF-1 testing is also offered in serum.

Why Test IGF-1?

Growth Hormone (GH) Excess or Deficiency

Growth hormone (GH) stimulates IGF-1 production in the liver, and therefore IGF-1 levels reflect average daily levels of GH2. Unlike GH, levels of IGF-1 do not fluctuate throughout the day. Other hormones affecting IGF-1 levels include thyroxine, cortisol and sex steroids3. The steady decline in GH production with increasing age, subsequent to the pubertal growth spurt, tends to be associated with an age-dependent decrease in IGF-1 levels. IGF-1 testing can be useful for patients with symptoms of premature aging associated with adult GH deficiency. It is particularly important to test for IGF-1 whenever GH supplementation is being used to treat premature aging or to improve wellbeing, so that levels are kept within the expected physiological range4,5.

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