There is no single normal IGF-1 number. A value of 150 ng/mL is low-normal for a 25-year-old and solidly mid-range for a 65-year-old. The age-adjusted range is the only one that means anything.
IGF-1 is the main lab marker for the GH axis, and its normal range depends almost entirely on age. IGF-1 declines steadily from the 20s onward, so a result that is healthy for someone in their 60s would be low for someone in their 20s. Reading IGF-1 without the age-adjusted reference range is the most common way the number gets misinterpreted.
- IGF-1 is age-dependent and falls steadily across adult life
- A normal result is defined only against an age-adjusted reference range
- Reference ranges are assay-specific, so the lab report range is the one that governs
- Low-normal IGF-1 with symptoms is the typical threshold for considering sermorelin
- IGF-1 is retested at 90 days to confirm dose response
What IGF-1 Measures
IGF-1, insulin-like growth factor 1, is produced mainly by the liver in response to GH. It carries out most of the downstream effects associated with GH, and because it stays stable across the day, it is a far more practical marker than GH itself, which is released in pulses and is difficult to capture on a single draw. When a provider evaluates the GH axis, IGF-1 is the number they read first.
Typical IGF-1 Ranges by Age
The table below shows representative adult IGF-1 reference ranges by decade in ng/mL. These are typical values for orientation only. Reference intervals are assay-specific and vary between laboratories (Bidlingmaier et al., 2014 [1]), so the range printed on your own lab report is always the one that applies to your result.
| Age | Typical IGF-1 range (ng/mL) |
|---|---|
| 21 to 30 | 117 to 329 |
| 31 to 40 | 109 to 284 |
| 41 to 50 | 94 to 252 |
| 51 to 60 | 81 to 225 |
| 61 to 70 | 69 to 200 |
| 71 to 80 | 57 to 195 |
IGF-1 assays differ in calibration, so a result must be compared against the reference range supplied with that specific test. Use the ranges above to understand the age trend, not to overrule the interval on your report.
What Low-Normal Actually Means
A result inside the reference range is not automatically optimal. Low-normal means the value sits in the bottom portion of the age-adjusted range. For an adult with the symptom cluster of GH decline, a low-normal IGF-1 is often the point at which a prescribing physician will consider sermorelin, because it indicates the GH axis is operating near the low end of normal for that age. A frankly low result below the range strengthens the case further.
- Below range: GH axis output is low for age
- Low-normal: bottom of the age range, the common threshold for treatment when symptoms are present
- Mid-range: typical for age
- Upper range: higher GH axis output; values above range warrant evaluation, not treatment
What Can Shift an IGF-1 Result
Several factors move IGF-1 independent of the GH axis, which is why context matters when reading a single value. Accounting for these prevents both false reassurance and false alarm.
- Estrogen: oral estrogen lowers hepatic IGF-1 more than transdermal estrogen
- Thyroid: hypothyroidism reduces the liver capacity to produce IGF-1 in response to GH
- Testosterone: low testosterone in men can lower IGF-1
- Nutrition: fasting, low protein intake, and acute illness lower IGF-1
- Liver function: because IGF-1 is hepatic, liver disease reduces it
How IGF-1 Guides Sermorelin Therapy
IGF-1 frames the entire sermorelin protocol. A baseline draw establishes whether treatment is clinically indicated. The same marker is then retested at approximately 90 days, the point at which IGF-1 stabilizes at its new level, to confirm the dose is producing a response and to guide titration. A protocol run without a baseline and a 90-day retest is operating without the one objective measure of whether it is working.
Bottom Line
IGF-1 only makes sense against an age-adjusted, assay-specific reference range. The ranges in this guide show the downward trend across adult life, but the interval on your own report is what governs your result. Low-normal IGF-1 with symptoms of GH decline is the usual threshold for considering sermorelin, and the 90-day retest is what confirms the protocol is working.
Frequently Asked Questions
What is a normal IGF-1 level by age?
IGF-1 declines steadily with age, so the normal value depends on age band. Representative adult ranges in ng/mL are roughly 117 to 329 at age 21 to 30, 94 to 252 at 41 to 50, and 69 to 200 at 61 to 70. These are orientation values only. IGF-1 assays are lab-specific, so the reference range printed on your own report is the one that defines a normal result for you.
What does a low IGF-1 level mean?
A low IGF-1 means GH axis output is below the age-adjusted reference range. In an adult with symptoms such as poor slow-wave sleep, increased visceral fat, and reduced lean mass, a low or low-normal IGF-1 supports a clinical picture of GH decline. Because thyroid function, testosterone, nutrition, and liver health also affect IGF-1, a low result is interpreted in context, not in isolation.
Why is IGF-1 used instead of measuring growth hormone directly?
GH is released in pulses and changes rapidly through the day, so a single GH draw can miss the picture entirely. IGF-1 is produced by the liver in response to GH and stays stable across the day, which makes it a far more reliable single-draw marker of GH axis activity. This is why IGF-1 is the primary screening and monitoring test.
What IGF-1 level qualifies for sermorelin?
There is no universal cutoff. The common threshold is a low or low-normal IGF-1 against the age-adjusted range in an adult who also has symptoms of GH decline. A frankly low result below the range strengthens the case. The prescribing physician interprets the baseline value alongside symptoms and other hormones rather than applying a fixed number.
How much should IGF-1 rise on sermorelin?
IGF-1 is retested at approximately 90 days, when it stabilizes at its new level, to confirm the dose is producing a response. The goal is to move IGF-1 into a healthier position within the age-adjusted range, not to exceed it. The size of the appropriate increase depends on the baseline value and is used to guide dose titration.
References
- Reference intervals for insulin-like growth factor-1 (IGF-1) from birth to senescence JCEM, 2014. PMID: 24606072. https://pubmed.ncbi.nlm.nih.gov/24606072/
- Human growth hormone and human aging (age-related IGF-1 decline) Endocrine Reviews, 1993. PMID: 8491152. https://pubmed.ncbi.nlm.nih.gov/8491152/
- Endocrine effects of GHRH-(1-29)-NH2 in age-advanced subjects (90-day IGF-1 response) JCEM, 1997. PMID: 9141536. https://pubmed.ncbi.nlm.nih.gov/9141536/
