An IGF-1 test is a blood test that checks for growth hormone disorders. It measures insulin-like growth factor 1, a protein your liver produces in response to growth hormone. Because growth hormone itself fluctuates throughout the day based on your diet and activity, it’s unreliable to measure directly. IGF-1 levels stay much more stable, making this test the most practical way to assess whether your body is producing too much or too little growth hormone.
How IGF-1 Relates to Growth Hormone
Your pituitary gland, a small structure at the base of your brain, releases growth hormone into your bloodstream. That hormone travels to your liver, which responds by producing and secreting IGF-1. IGF-1 then circulates through the body and carries out most of growth hormone’s actual work: building bone, maintaining muscle mass, and supporting tissue repair.
Think of growth hormone as the signal and IGF-1 as the messenger that delivers the instructions. Measuring IGF-1 gives a reliable snapshot of how much growth hormone your body has been producing over time, rather than catching it at a random high or low point during the day.
Conditions the Test Detects
Doctors order an IGF-1 test when they suspect growth hormone is either too high or too low. The specific conditions it helps identify depend on whether the result comes back above or below the expected range for your age.
Low IGF-1
A low result points toward growth hormone deficiency. In children, this can cause noticeably slower growth and significantly shorter stature compared to peers of the same age. In adults, growth hormone deficiency shows up differently: reduced muscle mass, lower bone density, and increased body fat. A low IGF-1 result has high specificity for growth hormone deficiency, meaning if the level is clearly below normal, the diagnosis is likely correct. However, the test is less sensitive, so a normal result doesn’t completely rule out the condition. Additional stimulation tests are often needed to confirm the diagnosis.
A rare genetic condition called Laron syndrome also produces low IGF-1 levels. In this case, the pituitary gland makes plenty of growth hormone, but the body can’t use it properly, so the liver never gets the signal to produce IGF-1.
High IGF-1
An elevated result suggests the body is producing too much growth hormone. In children, this causes gigantism, marked by extreme height for their age along with unusually large hands and feet. In adults, excess growth hormone causes acromegaly, which leads to thickened bones and gradual enlargement of the hands, feet, and facial features. Acromegaly develops slowly, and the physical changes are often so gradual that patients and their families don’t notice them for years. The average delay between disease onset and diagnosis is 4 to 10 years, and that prolonged delay is associated with more serious health complications.
The Endocrine Society recommends IGF-1 testing for anyone showing classic facial or hand/foot enlargement, but also for patients who develop a cluster of related conditions: sleep apnea, high blood pressure, type 2 diabetes, joint pain, carpal tunnel syndrome, or excessive sweating. An elevated IGF-1 result in someone with these features is typically enough to confirm the diagnosis, though a glucose tolerance test may be used for additional confirmation.
What Can Skew Your Results
IGF-1 levels don’t only reflect growth hormone status. Several other conditions can push results lower or higher independently, and your doctor needs to account for these when interpreting the test.
Severe malnutrition and other catabolic states, including major surgery recovery and chronic illnesses like cystic fibrosis, drive IGF-1 levels down significantly. These levels improve once nutrition is restored or the acute illness resolves. Liver disease also suppresses IGF-1 because the liver is where the protein is manufactured. Even in early-stage cirrhosis, IGF-1 production can drop as liver function declines. In some cases of compensated cirrhosis, blood levels may appear normal even though the body isn’t using IGF-1 effectively.
Insulin resistance and metabolic syndrome are linked to lower IGF-1 as well. Chronically high insulin levels appear to suppress IGF-1 production in the liver, so people with poorly controlled diabetes or significant abdominal obesity may show reduced levels that don’t reflect a pituitary problem at all.
On the other end, IGF-1 naturally rises during puberty and pregnancy, so these need to be considered when evaluating results in teenagers or pregnant individuals.
How Normal Ranges Change With Age
IGF-1 levels peak during puberty and early adulthood, then decline steadily with age. This means results always need to be compared against age-specific reference ranges rather than a single universal number. In healthy adults ages 21 to 25, the typical range (5th to 95th percentile) runs from about 158 to 416 ng/mL. By ages 46 to 50, that range drops to roughly 73 to 235 ng/mL. By ages 71 to 75, it narrows further to about 66 to 203 ng/mL.
Because of this steady decline, a level that looks perfectly normal for a 25-year-old might be flagged as elevated for a 60-year-old. Labs report results alongside the appropriate reference range for your age, so you’ll see your number in context. For children under 3, reliable reference values haven’t been established because IGF-1 remains naturally low for the first 15 to 18 months of life.
How IGF-1 Is Used to Monitor Treatment
Beyond diagnosis, the IGF-1 test plays an ongoing role for anyone receiving growth hormone therapy. International guidelines recommend adjusting the dose of growth hormone replacement based on IGF-1 levels, with the goal of keeping them within the normal range for your age. For adults on stable doses, IGF-1 is typically checked every 6 to 12 months. For children, the target is maintaining levels within the normal age-appropriate range throughout treatment.
The test is equally important for monitoring acromegaly after treatment. Following surgery to remove a pituitary tumor, IGF-1 levels are usually rechecked at about 3 months. In the early weeks after surgery, IGF-1 may still be falling, so results from that window can be misleading. If follow-up results are borderline or don’t match other test findings, doctors will typically repeat the testing after another 3 to 4 months before making treatment decisions. In some cases, a different lab assay may be used to confirm a questionable result.
What to Expect From the Test
The IGF-1 test is a standard blood draw. No fasting is required, and you don’t need to stop any medications beforehand. Because IGF-1 levels remain stable throughout the day, the timing of the blood draw doesn’t significantly affect results. The sample is sent to a lab and results are typically available within a few days. The test itself carries no risks beyond the minor discomfort of a needle stick.