IGF-1 Blood Test: High & Low Levels by Age Explained

The IGF-1 blood test (somatomedin C) is the best marker of growth hormone activity. Learn normal IGF-1 levels by age and sex, and what high (acromegaly) or low (GH deficiency) means.

Published July 20, 202611 min readWritten by the Blood Analysis Team · Reviewed and verified by Julien Priour

IGF-1 (insulin-like growth factor 1, also called somatomedin C) is a hormone made by the liver under the control of growth hormone (GH). Because its level stays steady through the day, IGF-1 is the best blood marker of GH activity — which makes it the first-line screening test for growth hormone disorders. This guide covers normal IGF-1 levels by age and sex, what a high result (acromegaly) or a low result (GH deficiency) means, the causes worth chasing, and why IGF-1 is only meaningful against age- and sex-matched reference ranges. IGF-1 is best read within a broader hormone panel, alongside markers such as cortisol and prolactin.

Key takeaways

IGF-1 is made by the liver in response to growth hormone (GH); because its level is stable, it integrates GH's pulsatile secretion and is the best single reflection of GH activity.¹²
High IGF-1 most often signals excess GH: acromegaly in adults, gigantism in children, usually caused by a benign pituitary adenoma.³¹
Low IGF-1 points to GH deficiency (short stature in children, adult GH deficiency), but also to undernutrition, liver disease, poorly controlled diabetes, hypothyroidism, or prolonged fasting.⁴⁵
Values depend heavily on age, sex, and puberty (a peak in adolescence, a steady decline with age), so IGF-1 is only interpreted against age- and sex-matched norms.⁶⁷
The unit is ng/mL (identical to µg/L). Ranges vary by lab and assay method — always compare against the one printed on your report.⁶⁸
IGF-1 is not a cancer marker and not an "anti-aging" test: supplementing with GH or IGF-1 outside a medical indication is dangerous and not recommended.⁹

What is IGF-1?

IGF-1 is a protein hormone produced mainly by the liver. Its production is driven by growth hormone (GH), which is released by the pituitary gland at the base of the brain. In simple terms, GH gives the signal and IGF-1 carries out much of its work — driving the growth of bone and tissue and shaping metabolism.²¹

Its clinical value comes from one point of physiology. GH is released in bursts (pulses), mostly at night, so a single GH measurement can be high or nearly undetectable depending on timing and rarely means much on its own. IGF-1, by contrast, integrates that secretion over hours and stays steady through the day. That is why one IGF-1 blood draw tells you far more about overall growth hormone activity than a random GH level.¹²

IGF-1 is not insulin. Despite the name, IGF-1 is not insulin (which controls blood glucose). It resembles insulin structurally — hence "insulin-like" — but its main job is growth.

Why the test is done

IGF-1 is not a routine test. Your clinician orders it in targeted situations, almost always to explore growth hormone.³²

Suspected acromegaly in adults: features such as coarsening facial features, enlarging hands and feet (rising ring or shoe size), headaches, excess sweating, and joint pain. IGF-1 is the first test ordered.³¹
Suspected gigantism in a child or adolescent (excessive, rapid growth).³
Growth failure in a child, to screen for growth hormone deficiency.⁴
Adult GH deficiency work-up (fatigue, reduced muscle mass, impaired quality of life), on specialist advice.⁴
Treatment monitoring: after surgery for a pituitary adenoma, on GH-lowering therapy, or to fine-tune growth hormone replacement — IGF-1 helps confirm the dose is neither too low nor too high.¹⁴

Outside these settings, IGF-1 adds little. It is not a general screening test and not a longevity number to watch in a healthy person.⁹

Do you need to fast?

In most cases you do not need to fast for an IGF-1 test: the level does not swing with meals the way blood glucose does. One caveat matters — prolonged fasting or undernutrition genuinely lower IGF-1 and can produce a falsely low result. Follow the exact instructions on your order and mention any restrictive diet (see Do you need to fast before a blood test?).⁴⁶

Normal ranges

There is no single normal value for IGF-1: it depends closely on age, sex, and pubertal stage. The level peaks at puberty, then declines steadily with age. For that reason, labs often report the result as a standard deviation score (SDS or z-score), which compares your value to a population of the same age and sex.⁶⁷

Below are indicative ballpark ranges in healthy people, in ng/mL (= µg/L). They vary widely by lab and assay — don't use them to self-interpret.

Age group	Indicative IGF-1 (ng/mL = µg/L)
Prepubertal child (~6–10 y)	~80 – 300
Puberty (~12–16 y, peak)	~200 – 800
Young adult (~20–30 y)	~115 – 360
Adult (~30–50 y)	~90 – 280
Older adult (~50–70 y)	~75 – 230
Elderly (>70 y)	~60 – 200

Good to know: these are reference points, not official cut-offs. Actual values differ between labs depending on the assay method (immunoassays are not perfectly standardized) and vary somewhat by sex. Only your clinician interprets the result against your age, pubertal status, and clinical picture.⁶⁷⁸

Understanding your results

IGF-1 is always read against the age- and sex-matched norm, and rarely alone: it is the GH–IGF-1 pair that guides the diagnosis.

High IGF-1

A clearly high IGF-1 (above the upper limit for age) points above all to excess growth hormone:¹³

Acromegaly in adults: excessive GH production, most often from a benign pituitary adenoma, causing gradual enlargement of the hands, feet, and facial features.
Gigantism in a child or adolescent, when that excess occurs before growth is complete.

Here IGF-1 is the screening test: international guidance holds that, in someone with typical features, an IGF-1 clearly above the age-specific norm confirms acromegaly. It is then confirmed with a dynamic test — an oral glucose tolerance test (OGTT), which should normally suppress GH; failure to suppress confirms the excess.¹ A modestly high IGF-1 may also reflect puberty, pregnancy, or other physiologic states — your clinician sorts this out.

Low IGF-1

A low IGF-1 (below the age-specific limit) can reflect growth hormone deficiency, but not only that:⁴⁵

GH deficiency: in children, it can cause short stature and growth failure; in adults, it is linked to fatigue and changes in body composition. A single low IGF-1 is not enough to diagnose it — the diagnosis rests on GH stimulation tests.⁴
Common false lows: undernutrition or prolonged fasting, liver disease (the organ that makes IGF-1), poorly controlled diabetes, hypothyroidism, or any serious illness can lower IGF-1 without true pituitary deficiency. These must be ruled out first.⁴⁶

So a low IGF-1 is not cause for alarm: it needs context (diet, liver, thyroid, medications) before it means anything.

IGF-1, cancer, and "anti-aging": the myths to drop

IGF-1 is not a tumor marker — it is not used to screen for cancer. It's true that, in large population studies, a high IGF-1 has been associated with a slightly higher risk of some age-related diseases, but that link is statistical and does not make IGF-1 an individual cancer test.⁹

Above all, IGF-1 is not an "anti-aging" test. The idea that a higher level makes you "younger" is false and even misleading: recent data suggest that a high IGF-1 in older people is associated with more risk, not less.¹⁰⁹ Supplementing with growth hormone or IGF-1 outside a specific medical indication is dangerous (diabetes, joint pain, cardiovascular and metabolic harm) and not recommended.

What affects your IGF-1

Many things move IGF-1 apart from pituitary disease: age (a steady fall), sex, pubertal stage, nutritional status (fasting and undernutrition drop it), liver function, diabetes control, the thyroid, pregnancy (higher levels), and the lab's assay method, which is still imperfectly standardized between techniques.⁶⁷ Tell your clinician about your medications, diet, and medical history — they change the interpretation.

Recent research

According to recent PubMed-indexed publications:

A numeric threshold for acromegaly. The 2023 international consensus on acromegaly refined the biochemical criteria: in a person with typical features, an IGF-1 above ~1.3 times the age-specific upper limit of normal confirms the diagnosis, with IGF-1 remaining the anchor for treatment monitoring.¹ (Giustina A et al., Pituitary, 2023 — DOI.)
GH deficiency diagnosis, clarified. A 2025 Delphi consensus from the GH Research Society notes that a low IGF-1 is diagnostic of GH deficiency mainly when the whole pituitary is affected, but that in most cases the diagnosis still requires a GH stimulation test — IGF-1 alone is not enough.⁴ (Arlien-Søborg MC et al., Pituitary, 2025 — DOI.)
Standardizing reference values. Several recent studies rebuilt age- and sex-specific reference intervals, stressing that these norms also depend on ethnicity and assay method — which is why your result should be compared to the range of the lab that measured it.⁶⁷
IGF-1 and aging. In very large cohorts (including the UK Biobank), the relationship between IGF-1 and health is U-shaped: both low and high levels carry excess risk, and a high level in older people predicts more mortality and age-related disease — the opposite of an IGF-1 that "keeps you young."⁹¹⁰

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your IGF-1 interpreted by AI DiagMe

An IGF-1 level is never read alone: its meaning depends on your age, sex, pubertal status, nutrition, and the pair it forms with growth hormone. That cross-reading is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

What is an IGF-1 blood test?

It measures insulin-like growth factor 1 (somatomedin C), a hormone made by the liver in response to growth hormone. Because its level is stable, it serves as a faithful reflection of GH activity.

What is a normal IGF-1 level?

There is no single value: it depends on age, sex, and puberty, peaking in adolescence and falling with age. As a rough guide, adults often sit between ~90 and 280 ng/mL (= µg/L), but only the age-matched norms of your lab matter.

What does a high IGF-1 mean?

Most often excess growth hormone: acromegaly in adults, gigantism in children, usually from a benign pituitary adenoma. The diagnosis is confirmed with a suppression test (oral glucose tolerance test). A modest rise can also reflect puberty or pregnancy.

What does a low IGF-1 mean?

It can suggest growth hormone deficiency, but also undernutrition, prolonged fasting, liver disease, poorly controlled diabetes, or hypothyroidism. A single low value is not enough — GH deficiency is confirmed with stimulation tests.

Do I need to fast for an IGF-1 test?

Usually no. But prolonged fasting or undernutrition genuinely lower IGF-1, so follow your order and mention any restrictive diet.

Is IGF-1 a cancer marker?

No. It is not a tumor marker and is not used to screen for cancer. Some studies show a statistical association between high IGF-1 and certain diseases, but that does not make it an individual cancer test.

Is IGF-1 an "anti-aging" test? Can I supplement?

No. Raising your IGF-1 does not make you "younger" — in older adults, a high level is linked to more risk. Supplementing with GH or IGF-1 outside a medical indication is dangerous and not recommended.

Why measure IGF-1 instead of GH directly?

Because GH is released in bursts through the day, so a single measurement is unreliable. IGF-1 is stable, integrates that secretion, and better reflects overall growth hormone activity.

Bottom line

IGF-1 (somatomedin C) is made by the liver in response to growth hormone — and because its level is stable, it is the best blood marker of GH activity and the screening test for growth disorders. Remember that a high IGF-1 mainly points to acromegaly (or gigantism in children), confirmed with a suppression test, while a low IGF-1 can mean GH deficiency but also undernutrition, liver, diabetes, or thyroid problems. Above all, values depend on age, sex, and puberty and vary by lab, so they only make sense against matched norms. IGF-1 is neither a cancer marker nor an "anti-aging" test. No value is read alone — it's your whole panel and context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official sources and peer-reviewed publications (PubMed) used for this guide:

Giustina A, Biermasz N, Casanueva FF, et al. Consensus on criteria for acromegaly diagnosis and remission. Pituitary, 2023. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹
Endocrine Society — Acromegaly and Growth Hormone. endocrine.org ↩ ↩² ↩³ ↩⁴
MedlinePlus (U.S. National Library of Medicine, NIH) — Insulin-Like Growth Factor 1 (IGF-1) Test. medlineplus.gov ↩ ↩² ↩³ ↩⁴ ↩⁵
Arlien-Søborg MC, Radovick S, Boguszewski MCS, et al. Consensus and controversies about diagnosing GH deficiency: a Delphi survey by the GH Research Society. Pituitary, 2025. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹
Testing.com — Insulin-Like Growth Factor 1 (IGF-1) Test. testing.com ↩ ↩²
Kim B, Cho Y, Ku CR, et al. Establishment of Reference Intervals for Serum Insulin-Like Growth Factor I in Korean Adult Population. Endocrinol Metab (Seoul), 2020. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸
Isojima T, Shimatsu A. Proposed reference intervals of serum insulin-like growth factor-1 (IGF-1) levels in older Japanese populations. Endocr J, 2023. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵
Mayo Clinic Laboratories — Insulin-Like Growth Factor 1 (IGF-1), Serum. mayocliniclabs.com ↩ ↩²
Zhang WB, Ye K, Barzilai N, Milman S. The antagonistic pleiotropy of insulin-like growth factor 1. Aging Cell, 2021. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵
Zhang WB, Aleksic S, Gao T, et al. Insulin-like Growth Factor-1 and IGF Binding Proteins Predict All-Cause Mortality and Morbidity in Older Adults. Cells, 2020. PubMed · DOI ↩ ↩²