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Energy & Metabolism

IGF-1 (Insulin-like Growth Factor 1)

IGF-1 is a hormone that carries the day-to-day signal of your growth hormone — the liver makes it whenever growth hormone is active. Because its level stays steady through the day, while growth hormone itself spikes and dips, it is a handy mirror of your average growth-hormone activity. It is read against an age-matched range, since levels fall naturally as we get older.

Targeted Testing
CategoryEnergy & Metabolism
Reference rangeSee your report
Evidence○Targeted Testing
Last updated3 July 2026
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What is igf-1 (insulin-like growth factor 1)?

Insulin-like growth factor-1 (IGF-1) is a hormone produced mainly by the liver in response to signals from growth hormone (GH). Together, IGF-1 and growth hormone are vital for normal bone and tissue growth and development throughout life. Unlike growth hormone — which surges and dips unpredictably through the day, making it hard to measure reliably — the blood IGF-1 level is stable and does not fluctuate throughout the day. This makes IGF-1 a useful and practical proxy for overall growth hormone activity: a single blood draw can give your GP a reliable picture of your average GH output, without having to time the test to a particular hour. IGF-1 levels change with age, declining from their peak in adolescence through adulthood, so your result is compared to a reference interval matched to your age rather than a single universal number.

Why is it tested?

Because IGF-1 reflects growth hormone activity more reliably than GH itself, it is commonly used to investigate suspected growth hormone problems, and your GP or specialist may order it for that reason. Your GP or specialist may order it when investigating suspected growth hormone deficiency, where the pituitary is not producing enough GH, or where GH excess is suspected, as in acromegaly or gigantism. Acromegaly is a rare disorder in adults caused by the pituitary gland producing too much growth hormone, usually because of a benign (non-cancerous) tumour in the gland. IGF-1 is a diagnostic feature of acromegaly because high concentrations of growth hormone act partly by increasing production of insulin-like growth factors.

Reference range (Australia)

Use the age-related reference interval printed on your report — IGF-1 is compared against an age-matched range and read together with the clinical picture ng/mL

IGF-1 is stable through the day (unlike growth hormone) but changes with age, so it is compared to an age-matched interval.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

A below-range IGF-1 may reflect growth hormone deficiency, where the pituitary is not producing enough GH, or it can be related to poor nutrition, significant illness, or the normal decline that comes with ageing. Your GP will interpret a low result in the context of your age, the age-matched interval, and any symptoms you have.

If your level is in range

An IGF-1 within the age-matched reference interval on your report suggests your growth hormone axis is functioning within the expected range for your age. No specific follow-up is usually needed for the IGF-1 result alone; your GP will consider it in the context of your clinical picture.

If your level is high

Acromegaly is rare, so a single raised IGF-1 does not mean you have it. A high IGF-1 can reflect elevated growth hormone activity, and it is one of the features clinicians use when investigating acromegaly, but your GP or specialist reads it against the full clinical picture and usually orders confirmatory tests rather than concluding from IGF-1 alone.

What can affect your result

Age is the biggest driver: IGF-1 peaks in adolescence and then declines steadily through adulthood, so what is normal at 20 is different from what is normal at 60. Your report's reference interval will already reflect your age group. Nutrition matters too — IGF-1 production requires adequate protein and energy intake, so significant malnutrition or prolonged illness can lower it even when the pituitary is working normally. Poor sleep can reduce the GH pulses that drive IGF-1 production. Conversely, GH excess from a pituitary tumour raises IGF-1. Because IGF-1 is a downstream product of GH activity in the liver, any condition affecting the liver may also affect IGF-1 levels. Your GP will factor in your overall health picture when interpreting the result.

When to act

An IGF-1 result outside the age-matched range is a prompt for a conversation with your GP rather than cause for immediate concern. If the result is high, they will consider whether any symptoms — such as changes in facial features, hand or foot size, or joint pain — warrant specialist review. If it is low, they will factor in your age, nutrition, and any relevant health history. Because IGF-1 is a specialised test, an unexpected result typically leads to a discussion with an endocrinologist (a specialist in hormone conditions) before any firm conclusions are drawn. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

IGF-1 — insulin-like growth factor-1 — is a hormone produced by the liver in response to growth hormone (GH). Testing IGF-1 is the standard way to assess overall GH activity, because IGF-1 stays at a steady level through the day while GH itself spikes and dips unpredictably. A single blood draw for IGF-1 therefore gives a reliable snapshot of your average growth hormone output.

Growth hormone is secreted in irregular bursts throughout the day, which makes a single blood sample for GH unreliable — the result depends heavily on timing. IGF-1 does not have this problem: unlike GH, the blood IGF-1 level is stable and does not fluctuate throughout the day. This makes it a more practical and more dependable test for understanding your GH axis.

A high IGF-1 can reflect elevated growth hormone activity. One of the clinical uses of the test is to detect GH excess in suspected cases of acromegaly — a rare condition in adults caused by the pituitary gland producing too much growth hormone, usually due to a benign tumour. A high IGF-1 is one of the features clinicians use when investigating acromegaly. That said, a raised result needs to be interpreted alongside your clinical picture; your GP or a specialist will determine whether further investigation is needed.

Acromegaly is a rare disorder in adults caused by the pituitary gland producing too much growth hormone, usually because of a benign (non-cancerous) tumour in the gland. Because it is rare, a single above-range IGF-1 does not mean you have acromegaly — the result is one input into a clinical assessment that includes symptoms and other tests. If your GP considers acromegaly a possibility, they will refer you to a specialist for further evaluation.

Yes — IGF-1 declines with age, so there is no single normal number that applies across all adults. Your report will include an age-matched reference interval specific to your age group, and that is the range your GP uses to interpret your result. Comparing an older adult's IGF-1 to a young adult's range, or vice versa, would not be meaningful.

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