Definition: IGF-1 (insulin-like growth factor 1) is a hormone that carries out many of the effects of growth hormone (GH). Growth hormone levels swing through the day, but IGF-1 is more stable, so MedlinePlus says measuring IGF-1 is a reliable way to track GH in the body. It is also called somatomedin C.
Why it shows up on labs when you track doses
IGF-1 is the main lab tied to growth hormone treatment. The Genotropin (somatropin) label says adult doses are adjusted based on clinical response and serum IGF-I, and should be lowered if IGF-I rises above the age- and sex-specific normal range.
The Egrifta SV (tesamorelin) label says the drug stimulates GH production and raises serum IGF-1, that the effects of long-term high IGF-1 are unknown, and that IGF-1 should be monitored during treatment. This is why IGF-1 often comes up with growth hormone secretagogues.
MedlinePlus says no special preparation is needed for the test.
Common mix-ups
- Age changes the normal range. MedlinePlus says IGF-1 is low in childhood, peaks during puberty and falls in adulthood. A result only makes sense against an age- and sex-matched range.
- IGF-1 is not growth hormone. MedlinePlus describes it as a separate hormone that manages the effects of GH. Separate GH tests exist, such as stimulation and suppression tests.
- The lab test is not the drug. Increlex (mecasermin) is a man-made IGF-1 with the same amino acid sequence as the body's own. Its label limits it to children with severe primary IGF-1 deficiency, and says it is not a substitute for GH.
Each lab sets its own reference range, so read your result against the range printed on your own report, and talk with your clinician about what it means for you.
Read more on Dose Track: HGH guide · Tesamorelin guide · Logging lab results in Dose Track
General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
Why test IGF-1 instead of growth hormone?+
Growth hormone levels change through the day with diet and activity. IGF-1 is more stable, so MedlinePlus calls it a reliable way to track GH in the body.
Do I need to fast for an IGF-1 test?+
MedlinePlus says no special preparation is needed. If other tests are drawn at the same time, those may have their own fasting rules.
What is a normal IGF-1 level?+
It depends on age and sex, and each lab prints its own range. The Genotropin label refers to an age- and sex-specific normal range. Your clinician reads the result against that.