An IGF-1 blood test is the main screening test for growth hormone problems, because IGF-1 levels stay fairly steady through the day while growth hormone itself rises and falls. A low result in a child can point to growth hormone deficiency; a clearly high result in an adult with typical features can point to acromegaly. But IGF-1 is only meaningful when it is compared with the right reference range for your age and sex, and a long list of everyday factors, from pregnancy to liver disease to estrogen pills, can move it.
What IGF-1 is and why it is measured instead of growth hormone
IGF-1, or insulin-like growth factor 1, is a peptide hormone. UniProt’s protein record shows the active hormone is a 70-amino-acid chain structurally related to insulin. According to MedlinePlus, IGF-1 carries out many of growth hormone’s effects, and together they drive normal growth of bones and tissues. Growth hormone levels change throughout the day with diet and activity, while IGF-1 is more stable, so measuring IGF-1 is a reliable way to track growth hormone activity. Levels are low in childhood, peak during puberty and decline through adulthood.
The test is an ordinary blood draw, and MedlinePlus says no special preparation is needed. It is used to detect and monitor growth hormone deficiency, growth hormone insensitivity, gigantism in children and acromegaly in adults. MedlinePlus also notes that IGF-1 testing is not common for adults with vague symptoms such as fatigue, because other conditions are much more likely to explain them.
What a low or high result can mean
In a child, MedlinePlus says a lower-than-normal IGF-1 probably means growth hormone deficiency or insensitivity and usually leads to more testing, such as a growth hormone stimulation test. In an adult, a low result may simply reflect the normal age-related decline or another condition.
A high result can suggest gigantism in children or acromegaly in adults, most often caused by a tumor in the pituitary gland. Experts take care before calling it, though. A 2024 international acromegaly consensus published in Pituitary says that in a patient with typical features, an IGF-1 more than 1.3 times the upper limit of normal for age confirms the diagnosis. For borderline results, it recommends repeating IGF-1 using the same validated assay and possibly an oral glucose tolerance test, in which growth hormone should normally fall.
Everyday factors that can move the number
A 2026 review of acromegaly diagnosis in the Journal of Clinical Endocrinology and Metabolism lists conditions that can push IGF-1 results up or down and cause false-positive or false-negative readings:
- puberty and pregnancy
- poorly controlled diabetes
- liver disease and kidney insufficiency
- malnutrition and obesity
- oral estrogen or selective estrogen receptor modulators
The same review warns that IGF-1 results vary between assays and laboratories, and that reference ranges differ by age, sex and population. That is why the consensus recommends using the same well-validated assay for every follow-up measurement.
Questions to ask about your result
- Which age- and sex-specific reference range did the lab use, and how far outside it is my result?
- Could pregnancy, oral estrogen, diabetes control, liver or kidney function, or recent weight change be affecting it?
- If we repeat it, will it be done by the same lab and method?
- Is a stimulation or glucose suppression test needed to confirm what this suggests?
The everyday takeaway: bring a full list of your medicines, including any hormone pills, to the appointment, keep follow-up IGF-1 tests at the same lab where possible, and treat one out-of-range number as a reason for a careful conversation rather than a diagnosis. Because the signs of acromegaly develop slowly, the 2026 review notes the diagnosis is often delayed by 6 to 10 years, so if you notice gradual changes such as enlarging hands or feet or coarsening facial features, mention them to a clinician.
By The Everyday Brief · AI-assisted editorial. Drafted with AI research assistance; claims checked against the linked sources (fetched 2026-10-05 PT). Not medical advice.
Sources
- MedlinePlus (U.S. National Library of Medicine): IGF-1 (Insulin-like Growth Factor 1) Test
- Giustina A, et al. Consensus on criteria for acromegaly diagnosis and remission. Pituitary, 2024.
- Yogi-Morren D, Chanson P. Acromegaly diagnosis. Journal of Clinical Endocrinology and Metabolism, 2026.
- UniProt: P05019, Insulin-like growth factor 1 (human)