Insulin-like Growth Factor 1 (IGF-1) Test
The IGF-1 test measures insulin-like growth factor 1, the principal mediator of growth hormone action and a stable, integrated marker of GH activity that avoids the pulsatile variation of growth hormone itself. It is the first-line biochemical screen for acromegaly, where it is elevated, and a central marker in growth hormone deficiency, where it is low for age.
1
Biomarkers
Blood (serum)
Sample
2–4 business days
Turnaround
No
Fasting
What is the IGF-1 test?
The IGF-1 Test measures insulin-like growth factor 1, the principal mediator of growth hormone action and a stable, integrated marker of GH activity. Because growth hormone itself is secreted in pulses and fluctuates widely through the day, IGF-1 — with its long half-life and steady concentration — is the more practical single measure of the GH axis. In the diagnostic landscape, IGF-1 is the first-line biochemical screen for disorders of GH secretion. It is elevated in acromegaly and gigantism, where it serves as the principal screening test, and low for age in adult and childhood GH deficiency, where it contributes to diagnosis alongside dynamic GH testing. Its great advantage over random GH measurement is freedom from pulsatile variation, but its interpretation is entirely dependent on age- and sex-specific reference ranges, since levels fall markedly across the lifespan. IGF-1 is also affected by nutritional state and hepatic function, which must be considered, and dynamic GH testing remains necessary to confirm GH excess or deficiency.
What does the IGF-1 test measure?
Insulin-like growth factor 1 is a peptide hormone produced mainly by the liver under the stimulation of pituitary growth hormone (GH), and it mediates most of GH's anabolic and growth-promoting effects. Unlike GH, which is secreted in pulses with wide intraday swings, IGF-1 circulates bound to IGF-binding proteins with a long half-life, giving stable concentrations that reflect integrated GH activity. Levels peak in adolescence and decline progressively with age, and are influenced by nutritional and hepatic status.
Because it provides a stable, integrated measure of GH action, IGF-1 is the preferred single test for screening disorders of GH excess and deficiency. It is the key biochemical screen for acromegaly, where it is elevated, and a central marker in assessing GH deficiency, where it is low for age. Interpretation is wholly dependent on age- and sex-specific reference ranges, and IGF-1 is also reduced by malnutrition and significant hepatic disease independent of the GH axis.
Why is the IGF-1 test ordered?
- Screening for acromegaly in patients with characteristic features — acral enlargement, coarsening facial features, or associated metabolic findings
- Assessment of suspected growth hormone deficiency in adults with compatible clinical and biochemical features, alongside dynamic testing
- Evaluation of growth disorders in children, including short stature and suspected GH deficiency, within specialist assessment
- Monitoring of growth hormone replacement therapy to guide dosing within age-appropriate targets
- Monitoring of treatment response in acromegaly following surgery, medical therapy, or radiotherapy
- Investigation of pituitary disease where assessment of the GH axis is required as part of a broader pituitary workup
- Assessment of the GH axis in patients with known pituitary pathology or prior cranial irradiation
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
2–4 business days
Collection notes
No strict timing requirement, as IGF-1 lacks the pulsatility of GH. Document nutritional state, oestrogen therapy, pregnancy, and significant hepatic disease, as these affect levels. For serial monitoring, use the same laboratory and assay. # REVIEWER FLAG: Confirm any LabCorp/Access Medical Laboratories preparation requirements.
Specimen requirements
Minimum 0.5 mL serum. Separate serum from cells within 2 hours of collection.
What can affect IGF-1 results?
IGF-1 peaks in adolescence and declines progressively with age, and differs by sex, so age- and sex-specific reference ranges (ideally SDS) are essential; a raw value is uninterpretable without them.
Undernutrition, catabolic states, and prolonged fasting lower IGF-1 independent of GH secretion, as adequate nutrition is required for hepatic IGF-1 production.
Because IGF-1 is produced largely by the liver, significant hepatic dysfunction reduces levels regardless of GH status, complicating interpretation of the GH axis.
Oral oestrogen can lower IGF-1 by inducing hepatic GH resistance, so route and use of oestrogen should be considered in interpretation. # REVIEWER FLAG: Confirm handling of oral vs transdermal oestrogen effect.
Glycaemic control and intercurrent illness alter the GH-IGF-1 axis and IGF-binding proteins, shifting IGF-1 independent of primary pituitary pathology.
IGF-1 rises physiologically during puberty and in pregnancy, so these states must be accounted for when interpreting elevated values.
What do IGF-1 results mean?
Elevated
An IGF-1 above the age- and sex-specific range is the principal biochemical screen for acromegaly or gigantism and warrants confirmation, typically with an oral glucose tolerance test demonstrating failure of GH suppression, plus pituitary imaging. Physiological elevation occurs in puberty and pregnancy and should be excluded.
Normal
A normal age- and sex-adjusted IGF-1 makes significant GH excess unlikely and reduces the probability of GH deficiency, though it does not fully exclude deficiency, which may need dynamic testing where suspicion is high. Interpretation always rests on the age-specific reference, ideally expressed as an SDS.
Reduced
A low IGF-1 for age supports growth hormone deficiency but is not diagnostic alone, as malnutrition, hepatic disease, oral oestrogen, and systemic illness also lower it. Confirmation of GH deficiency requires dynamic stimulation testing in the appropriate clinical context.
Note: IGF-1 is meaningless without age- and sex-specific reference ranges, and standard deviation score reporting is preferred. It is a screening and monitoring marker, not a standalone diagnosis: GH excess and deficiency require confirmatory dynamic testing. Nutritional state, hepatic function, oestrogen, and glycaemic control all influence IGF-1 independent of the pituitary, and assay differences mean serial results should use the same method.
Frequently asked questions
It measures insulin-like growth factor 1, the main mediator of growth hormone action. Because it is stable and reflects integrated GH activity, it is the preferred single test of the growth hormone axis, avoiding the pulsatile variation of growth hormone itself.
How to access the IGF-1 test
The IGF-1 reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: June 3, 2026
Last reviewed: June 3, 2026
- Katznelson L, et al. Acromegaly: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. (2014)
- Molitch ME, et al. Evaluation and Treatment of Adult Growth Hormone Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. (2011)
- Clemmons DR. Consensus statement on the standardization and evaluation of growth hormone and insulin-like growth factor assays. Clin Chem. (2011)
- Brabant G, et al. Serum insulin-like growth factor I reference values for an automated chemiluminescence immunoassay. Horm Res. (2003)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.