What does an IGF-1 test measure?
An IGF-1 test measures insulin-like growth factor 1, a hormone that carries out many of growth hormone’s effects. When the pituitary releases growth hormone, the liver and other tissues respond by making IGF-1, which then acts on bone, muscle and other tissue. MedlinePlus describes IGF-1 and growth hormone working together to drive normal growth, and notes that the test is also called somatomedin C.
The test is a standard blood draw, and MedlinePlus lists no special preparation. In adults it is used mainly to look for growth hormone excess or deficiency and to monitor treatment that affects the growth hormone system.
Why measure IGF-1 instead of growth hormone?
Because a single growth hormone reading is close to meaningless. Growth hormone comes out in bursts, much of it during sleep, and MedlinePlus explains that its blood level changes through the day with diet and activity, so a standard blood test usually does not give useful information about it. A random draw could catch a peak or a trough.
IGF-1 smooths that out. Its level is far more stable from hour to hour, so one morning value reflects your average growth hormone activity much better than a growth hormone level would. When doctors need to test growth hormone directly, they use dynamic tests instead: a stimulation test that tries to provoke a release, or a suppression test that checks whether the pituitary shuts off when it should.
How does the normal range change with age?
IGF-1 is highest in the teenage years and declines steadily across adulthood, which is why there is no single normal range for men. A large reference study of more than 15,000 people from the U.S., Canada and Europe found that IGF-1 rises through childhood to a peak around age 15 and then decreases continuously for the rest of life.
| Life stage | Where IGF-1 typically sits |
|---|---|
| Mid-teens | Lifetime peak |
| Twenties | Falling from the peak |
| Thirties and forties | Continuing to decline |
| Fifties and beyond | Lower still, with each age band set lower |
By your thirties, a “normal” IGF-1 is already well below what it was at 18, and labs reflect this by printing age-banded reference ranges. The same study notes considerable differences between IGF-1 assay methods, so a number is only meaningful against the range of the lab and method that produced it. Some reports also give a standard deviation score, where 0 is the middle for your age and +2 or −2 marks the edges of the normal band.
A 52-year-old with an IGF-1 that would be low for a 25-year-old may be perfectly normal for his age. Our page on growth hormone decline in men covers what that decline does and does not explain.
What does a low or high result mean?
A low IGF-1 in an adult is often age, not disease. MedlinePlus notes that a lower result may be due to the normal age-related decrease or other conditions, and that IGF-1 testing is not common in adults with vague symptoms such as fatigue, since other disorders are far more likely to cause them. The Endocrine Society guideline on adult growth hormone deficiency states that the diagnosis usually has to be confirmed with stimulation testing, unless a structural or genetic cause is already proven.
A high IGF-1 points the other way. In adults, an elevated level can signal acromegaly, usually caused by a pituitary tumor, which shows up with enlarging hands and feet, coarsening facial features, heavy sweating and, in men, erectile dysfunction. That calls for a growth hormone suppression test and imaging, not a peptide.
How is IGF-1 used with peptide therapy?
IGF-1 is the main marker for judging growth-hormone-releasing peptides, before and during treatment. A baseline shows where you start relative to your age range, and later results show whether the peptide is working and whether it has pushed you too far. The tesamorelin (EGRIFTA SV) label tells clinicians to monitor IGF-1 during treatment and to consider stopping in people with persistent elevations.
Our page on IGF-1 levels on sermorelin or tesamorelin explains the targets and what changes when IGF-1 barely moves or overshoots, and our comparison of tesamorelin and sermorelin covers how the two differ. If you are wondering whether growth hormone itself is an option for aging, our answer on whether HGH is legal for anti-aging explains the rules.
Where IGF-1 fits at Ultimate Male
IGF-1 is part of the blood work that opens the clinic’s peptide therapy program, alongside metabolic and hormone markers, and it is rechecked at the six- to eight-week follow-up for men who start a growth-hormone-releasing peptide such as sermorelin. Draws are done on site at San Gabriel or Downey, with results in 24 to 48 hours.
Your provider reads the number against your age band and your goals. A result that is low for your age can support a peptide discussion; a result that is already high-normal, or above range, changes that conversation, and an unexpectedly high value leads to the right workup rather than treatment. Our page on blood work before peptide therapy lists the rest of the starting panel.
