IGF-1 Blood Test Explained: What It Measures and Why Clinicians Request It

This page is for educational purposes only and is not medical advice; consult a licensed physician about any laboratory result, symptom or treatment decision. Nothing below interprets an individual test value, and no reference ranges are offered as guidance — reference intervals are assay-specific and belong to the laboratory and the requesting clinician.

What IGF-1 Is and Where It Comes From

Insulin-like growth factor 1 (IGF-1, historically called somatomedin C) is a small peptide hormone structurally related to insulin. Most circulating IGF-1 is produced by the liver after stimulation by pituitary growth hormone (GH), with additional local production in many tissues. Because growth hormone itself is released in pulses and falls to very low values between pulses, reviews of the biochemical diagnosis of acromegaly have described IGF-1 as an integrated marker of growth hormone exposure rather than a snapshot of a single pulse (PMID 33803429).

IGF-1 does not circulate free in meaningful quantities. A review of insulin-like growth factor binding protein-3 described IGFBP-3 as the dominant carrier protein, forming a ternary complex with IGF-1 and the acid-labile subunit that governs how much peptide reaches tissue receptors (PMID 26522455). That binding biology matters for testing: assays must release IGF-1 from its binding proteins before measurement, and binding-protein shifts can move total IGF-1 without a parallel change in growth hormone secretion (PMID 26522455).

What the Test Actually Measures

An IGF-1 test is a blood test performed on serum or plasma, usually from a single venous draw. Unlike growth hormone, IGF-1 has a long circulating half-life and relatively modest within-day variation, which is why reviews of acromegaly diagnostics have positioned a single IGF-1 measurement as the usual first-line biochemical screen while growth hormone generally requires dynamic testing (PMID 41912292).

Two broad assay families appear in the clinical literature: immunoassays (including automated chemiluminescent platforms) and mass spectrometry–based methods. Reviews of the biochemical diagnosis of acromegaly have emphasised that different assays are not interchangeable and that results should be read against the normative data supplied for that specific method (PMID 33803429). A 2025 review of diagnostic challenges in acromegaly similarly discussed persistent assay standardisation problems as a source of discordant findings between laboratories (PMID 39757391).

Why Clinicians Request an IGF-1 Test

Suspected acromegaly or growth hormone excess

The most frequently described indication in the literature is suspected growth hormone excess. A 2026 review of the biochemical diagnosis of acromegaly described IGF-1 measurement as the central screening analyte, with confirmatory growth hormone testing used when the clinical picture and IGF-1 result do not align (PMID 41912292). The 2021 review on the same topic set out how IGF-1 and growth hormone results are combined, and discussed discordant cases in which one analyte is elevated and the other is not (PMID 33803429). Researchers writing the 2025 expert review also covered post-treatment monitoring, where IGF-1 is tracked after surgical, medical or radiation management of growth-hormone–secreting tumours (PMID 39757391).

Suspected growth hormone deficiency

IGF-1 is also requested at the opposite end of the axis. A review of the diagnosis of growth hormone deficiency described IGF-1 as one component of the diagnostic work-up, used alongside auxology, clinical history and provocative growth hormone stimulation testing rather than as a stand-alone test (PMID 20523017). That review noted that the diagnosis rests on combined evidence, since a single IGF-1 value does not by itself establish or exclude deficiency (PMID 20523017).

Research contexts

Outside endocrine diagnosis, IGF-1 appears as a research variable. A review of ageing, atherosclerosis and IGF-1 examined the hormone's relationship with vascular biology and the ageing process (PMID 22491965). An umbrella review of meta-analyses on obstructive sleep apnoea biomarkers surveyed candidate circulating markers studied for diagnosis and monitoring in that condition (PMID 36614858), and a 2025 biomarker review in Alzheimer's disease described how peripheral and central markers are being evaluated against amyloid and synaptic pathology (PMID 40864734). These are investigational contexts described in reviews, not established diagnostic uses.

Conditions Associated With High IGF-1: What Studies Report

The best-characterised cause of a persistently elevated IGF-1 in the published literature is growth hormone excess from a pituitary somatotroph tumour. The 2026 biochemical diagnosis review described elevated age- and sex-adjusted IGF-1 as the typical biochemical signature of acromegaly, prompting confirmatory testing and pituitary imaging (PMID 41912292). The 2025 expert review covered how diagnosis is frequently delayed because the physical changes of growth hormone excess accumulate slowly, and discussed individualised treatment pathways once the diagnosis is made (PMID 39757391).

Not every high value reflects a tumour. The 2021 review of biochemical diagnosis in acromegaly discussed physiological and analytical reasons why IGF-1 results can be misleading, including the need for appropriate normative comparison and recognition of discordant GH/IGF-1 patterns (PMID 33803429). Reviews of IGFBP-3 noted that the binding-protein environment shapes measured IGF-1, another reason a single number is not self-explanatory (PMID 26522455). The literature consistently frames interpretation as a clinical task for the requesting physician, not something a patient or a website can do from a number alone (PMID 41912292).

Conditions Associated With Low IGF-1: What Studies Report

Low IGF-1 is most directly linked to reduced growth hormone action. The review on diagnosing growth hormone deficiency described low IGF-1 as supportive but not sufficient evidence, because nutritional status, systemic illness and liver function also influence hepatic IGF-1 output (PMID 20523017). The IGFBP-3 review similarly discussed how growth-hormone–dependent binding protein levels are used alongside IGF-1 in paediatric assessment (PMID 26522455).

Catabolic and drug-related states also appear in the literature. A 2026 review of the management of glucocorticoid-induced myopathy addressed how chronic glucocorticoid exposure drives muscle protein loss and how clinicians assess and manage that complication (PMID 41951495). A review of ageing, atherosclerosis and IGF-1 discussed declining IGF-1 across the lifespan as a feature of normal ageing biology that complicates comparison against young-adult values (PMID 22491965).

Assay and Interpretation Caveats Described in Reviews

• Age and sex matter. Acromegaly diagnostic reviews stressed that IGF-1 must be compared against age- and sex-specific normative data from the same assay, because values fall with age (PMID 33803429, PMID 22491965).
• Assays differ. The 2025 expert review discussed standardisation gaps that can produce different results for the same sample on different platforms (PMID 39757391).
• Binding proteins interfere. Measured total IGF-1 depends on extraction of the peptide from IGFBP complexes, as reviewed in the IGFBP-3 literature (PMID 26522455).
• One analyte is rarely enough. Both acromegaly and growth hormone deficiency reviews described IGF-1 as part of a panel with dynamic testing and clinical assessment (PMID 41912292, PMID 20523017).
• Receptor biology is distinct from blood level. A 2019 update on Graves' disease discussed the IGF-1 receptor as a therapeutic target in thyroid eye disease, a mechanism separate from circulating IGF-1 concentration (PMID 30703831).

IGF-1 Testing in Veterinary Medicine

The analyte is used comparably in animals. A review of acromegaly in dogs and cats described IGF-1 measurement as a key screening test for growth hormone excess in companion animals, particularly in cats with insulin-resistant diabetes (PMID 33727117). A 2025 study of hypersomatotropism in diabetic cats in Australia examined how frequently growth hormone excess was identified in that population (PMID 41215559). These veterinary papers illustrate the same interpretive principle: researchers reported that IGF-1 screening is combined with clinical signs and imaging rather than read in isolation (PMID 33727117).

What the Literature Does Not Settle

Published reviews describe IGF-1 as a well-established endocrine analyte with unresolved edges. Assay harmonisation remained an open problem in the 2025 acromegaly review (PMID 39757391). The role of IGF-1 as a prognostic or risk marker outside endocrine disease is still investigational: reviews in vascular ageing (PMID 22491965), sleep apnoea biomarkers (PMID 36614858) and Alzheimer's disease biomarkers (PMID 40864734) discussed candidate markers without establishing routine clinical thresholds. Anyone with a result in hand should discuss it with the clinician who requested the test, who can place it against the laboratory's own reference data and the full clinical picture.

References

• Acromegaly: diagnostic challenges and individualized treatment (Expert Review of Endocrinology & Metabolism, 2025)
• Acromegaly: Biochemical diagnosis (Vitamins and Hormones, 2026)
• The Biochemical Diagnosis of Acromegaly (Journal of Clinical Medicine, 2021)
• Acromegaly in dogs and cats (Annales d'Endocrinologie, 2021)
• Hypersomatotropism in diabetic cats in Australia (Journal of Feline Medicine and Surgery, 2025)
• Insulin-like growth factor binding-protein-3 (IGFBP-3) (Best Practice & Research Clinical Endocrinology & Metabolism, 2015)
• Diagnosis of growth hormone deficiency (Endocrine Development, 2010)
• Aging, atherosclerosis, and IGF-1 (The Journals of Gerontology Series A, 2012)
• [Update Graves' disease 2019] (Deutsche Medizinische Wochenschrift, 2019)
• Potential Diagnostic and Monitoring Biomarkers of Obstructive Sleep Apnea — Umbrella Review of Meta-Analyses (Journal of Clinical Medicine, 2022)
• From Amyloid to Synaptic Dysfunction: Biomarker-Driven Insights into Alzheimer's Disease (Current Issues in Molecular Biology, 2025)
• [The management of glucocorticoid-induced myopathy] (La Revue de Médecine Interne, 2026)