If you have ever looked into growth hormone treatment or "GH peptides," you have probably seen IGF-1 mentioned. It is the lab number doctors lean on most when they think about growth hormone. This guide explains what IGF-1 is, why it gets checked, and how to talk about your results.
Key takeaways
- IGF-1 (insulin-like growth factor 1) is made mostly in the liver when growth hormone (GH) signals it. It carries out much of GH's work.
- GH goes up and down all day. IGF-1 is steadier, so it is the better snapshot of GH activity.
- Doctors use IGF-1 to help find GH disorders and to monitor treatments that raise GH.
- "Normal" depends on age. IGF-1 peaks in puberty and declines in adulthood.
- Higher is not better. IGF-1 kept above the normal range can cause real health problems.
What IGF-1 is
Your pituitary gland releases growth hormone in pulses, mostly during sleep. GH travels to the liver and other tissues and tells them to make IGF-1. IGF-1 then helps drive bone and tissue growth and plays a part in metabolism.
When IGF-1 rises, it also sends a "slow down" signal back to the brain, which reduces GH release. This feedback loop is one way the body keeps GH in balance.
Why doctors test IGF-1 instead of GH
According to MedlinePlus, GH levels change throughout the day with diet and activity, while IGF-1 stays relatively stable. One random GH test might catch a pulse or miss it. IGF-1 gives a more reliable picture of how much GH activity is happening over time.
That is why IGF-1 is often the first test. If something looks off, the doctor may order more specific tests:
- A GH stimulation test to check for GH deficiency
- A GH suppression test (often with a sugary drink) to check for GH excess
- An IGFBP-3 test, which measures the main protein that carries IGF-1
When IGF-1 gets checked
To look for a GH disorder
MedlinePlus lists IGF-1 as a test to help detect and monitor GH deficiency, GH insensitivity, gigantism in children and acromegaly in adults. Symptoms that might prompt testing include slow growth in children, or in adults, enlarged hands, feet and facial features, heavy sweating and a deepening voice.
Before and during treatment that affects GH
If a prescriber starts a treatment that raises GH, IGF-1 becomes a safety check. The FDA label for tesamorelin, an approved GHRH analog, tells prescribers to monitor IGF-1 during therapy and to consider stopping in people whose IGF-1 stays persistently high, especially if they are not getting much benefit. In the label's trials, almost half of people had IGF-1 above 2 standard deviations of normal at 26 weeks. The label also says the effects of long-term high IGF-1 are unknown.
Any provider who prescribes a GH-raising product, approved or compounded, should check a baseline IGF-1 and recheck it over time. Our post on GH secretagogues covers the different products.
What results may mean
Labs report IGF-1 with a reference range based on age (and sometimes sex). Some report a z-score or SDS, which shows how far you are from the average for your age. A value near 0 is average.
| Result | What it may point to | What usually comes next |
|---|---|---|
| Within range for age | GH activity in the expected range | Interpreted with symptoms and other labs |
| Low | GH deficiency or insensitivity, normal aging, or other causes such as liver disease or low body weight | Possible stimulation testing, imaging or other labs |
| High | GH excess such as acromegaly, often from a pituitary tumor, or a treatment raising GH | Possible suppression testing, MRI, or a treatment review |
A single number is not a diagnosis. Labs use different methods, so comparing results across labs can be tricky. Your provider will look at the whole picture.
Why "higher" is not a goal
Online forums sometimes treat a big IGF-1 jump as proof that a peptide "works." The medical view is more careful.
The NIDDK explains that in acromegaly, excess GH raises IGF-1 and can lead to type 2 diabetes, high blood pressure, heart disease, sleep apnea, arthritis, carpal tunnel syndrome and colon polyps. Treating acromegaly aims to bring GH and IGF-1 back to normal.
That does not mean a short-term rise from a prescribed treatment will cause acromegaly. It does mean the goal is a safe range for you, which is why monitoring matters. Rising blood sugar, swelling, joint pain or tingling in the hands are worth reporting.
Low IGF-1 with age
IGF-1 naturally declines after young adulthood. A lower number in a 60-year-old is often expected. True adult GH deficiency is usually caused by damage to the pituitary or nearby brain areas, for example from a tumor, surgery, serious head injury or radiation, according to the Endocrine Society. Diagnosing it usually needs more than an IGF-1 test.
So a "low-normal" result is not, by itself, a reason to start a GH product. Talk through what it means with your provider.
Getting ready for the test
MedlinePlus says no special preparation is usually needed. It is a standard blood draw from your arm. A few tips:
- Ask whether other tests in the same draw (like glucose or lipids) need fasting.
- Tell your provider about every medication, supplement or peptide you use, including ones bought online.
- Keep copies of your results so you can compare over time. The PepSteady app lets you log lab values next to your notes, and our follow-up appointment checklist helps you prepare questions.
Questions to ask your provider
- What is my IGF-1 compared with the range for my age?
- Is anything I take likely to change it?
- How often should we recheck it?
- What other labs, like glucose or A1c, should we watch along with it?
The bottom line
IGF-1 is the steady stand-in for growth hormone, which is why doctors check it to find GH disorders and to keep GH-related treatments safe. Normal depends on your age, and higher is not automatically better. Keep your results, share everything you take, and let a licensed provider interpret the numbers with you.
Sources
- IGF-1 (Insulin-like Growth Factor 1) Test, MedlinePlus
- Acromegaly, NIDDK
- Growth Hormone Deficiency, Endocrine Society
- EGRIFTA WR (tesamorelin) prescribing information, DailyMed
Frequently asked questions
Why do doctors test IGF-1 instead of growth hormone?
Growth hormone is released in pulses and changes a lot during the day, so one GH reading can be misleading. IGF-1 stays fairly steady, which makes it a more reliable picture of overall GH activity.
Is a higher IGF-1 always better?
No. IGF-1 that stays above the normal range for your age is linked to problems seen in acromegaly, such as diabetes, high blood pressure and heart disease. Doctors aim for a range that fits your age and situation, not the highest number possible.
Do I need to fast for an IGF-1 test?
MedlinePlus says no special preparation is usually needed for an IGF-1 blood test. Your provider or lab may give different instructions, especially if other tests are drawn at the same time, so follow what they tell you.