IGF-1 monitoring on GH-axis treatment
Why IGF-1 is the test, when to draw it on weekly GH, and what the labels say to do with it.
Checked 2026-10-22 Researched and written by Kymata Health Editorial · Sources cited inline Report an error
Short answer
GH itself comes in short pulses, so a single GH level says little; IGF-1, which GH makes the liver release, is steadier and is the test the labels use. Daily somatropin labels lower the dose when IGF-1 runs above the age- and sex-specific range. Weekly GH labels time the draw a few days after a dose; tesamorelin's sets a 3 SDS limit.
Why is IGF-1 measured instead of GH?
Because GH is released in bursts, about 14 a day when fed, and clears with a half-life of about 20 minutes, so a random GH sample can land on a peak or a trough (Hartman 1992, JCEM). IGF-1 follows the overall GH effect.
What do the daily somatropin labels say?
To lower the dose for side effects or when IGF-1 runs above the age- and sex-specific normal range (Norditropin label). The class warnings also note that IGF-1 may rise along with phosphorus, alkaline phosphatase and parathyroid hormone during treatment (Genotropin label).
When is IGF-1 drawn on a weekly growth hormone?
Levels rise and fall across the week, so the labels time the sample: 3 to 4 days after the previous Sogroya dose (Sogroya label) and 4 to 5 days after a Skytrofa dose (Skytrofa label). On Ngenla, IGF-1 peaks about 2 days after a dose and averages about 4 days after (Ngenla label).
What IGF-1 limit does the tesamorelin label set?
At 26 weeks, 47% of people on tesamorelin had IGF-1 above 2 SDS and 36% above 3 SDS. The label says to consider stopping when IGF-1 stays above 3 SDS, particularly when the visceral-fat response is weak (Egrifta WR label).
Frequently asked questions
Questions
- What does SDS mean?
- Standard deviation score: how far a result sits from the average for age and sex. +2 SDS is near the top of the normal range.
- Is IGF-1 also checked on mecasermin?
- Mecasermin is IGF-1 itself. Its label links tumours to doses that drove IGF-1 above the normal range.
Not medical advice This page summarises published labels and studies. It is not a recommendation to use any product; a clinician decides.