Blood test
IGF-1 test
IGF-1 test: what it measures, why a doctor orders it, how to prepare, and what a high or low result can mean - with private and NHS access routes in the UK.
Key facts
At a glance
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What it measures: insulin-like growth factor 1, the stable blood marker of growth hormone activity.
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Why it is ordered: to screen for acromegaly when features such as enlarging hands, feet or facial change appear, and to assess growth hormone deficiency in children and adults.
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No fasting or special preparation is needed for this test on its own.
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Reference ranges: expected values change markedly with age, so every result is read against an age-specific interval. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.
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A raised result raises the question of acromegaly and leads to confirmatory dynamic testing and pituitary imaging. A low result may indicate growth hormone deficiency, malnutrition or liver disease, and specialist confirmation is needed before treatment.
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Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.
The full picture
What this test tells you, and how to get it
The IGF-1 test measures insulin-like growth factor 1, the stable blood marker of growth hormone activity. Doctors most often request it to screen for acromegaly when features such as enlarging hands, feet or facial change appear, and to assess growth hormone deficiency in children and adults. No fasting or special preparation is needed for this test on its own. Expected values change markedly with age, so every result is read against an age-specific interval, and reference intervals genuinely differ between laboratories, so no single number should be treated as a universal cut-off - your result is always read against the range printed on your own report. Broadly, a raised result raises the question of acromegaly and leads to confirmatory dynamic testing and pituitary imaging, while a low result may indicate growth hormone deficiency, malnutrition or liver disease, and specialist confirmation is needed before treatment, and either finding is interpreted alongside your symptoms, medication and other results rather than in isolation. Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.
In the UK there are two routes to this test. Your NHS GP can arrange it free of charge when it is clinically indicated, though getting the appointment, the blood draw and the follow-up discussion can add days to weeks depending on local demand. Privately, the IGF-1 test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - as the front door to any growth hormone assessment. A private result still deserves a clinician's interpretation: an isolated number without context is where most confusion about blood tests begins.
A quiet reminder
This guide is for information, not medical advice.
Your own clinician knows your history and can tell you which parts apply to you. Reference ranges vary between laboratories - always read your result against the interval printed on your own report. Next review of this page: 2027-09-27.
Frequently asked
Common questions about IGF-1 test.
Quick, plain-English answers to what people ask us most.
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What is an IGF-1 test?
IGF-1 (insulin-like growth factor 1) is a hormone produced mainly in response to growth hormone. The blood test measures IGF-1 levels, which gives a more stable reflection of growth hormone activity over time than measuring growth hormone directly, since growth hormone itself fluctuates throughout the day.
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Why would a doctor order an IGF-1 test?
It is commonly used to investigate suspected growth hormone excess or deficiency, such as in acromegaly or growth disorders, and sometimes to monitor treatment for these conditions.
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Do I need to prepare for an IGF-1 test?
Fasting is often recommended, and your clinic may advise avoiding intense exercise the day before, as this can affect results. Specific instructions will be given based on why the test is being done.
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What happens during the test?
It is a simple blood draw taken from a vein, similar to a routine blood test.
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How long do IGF-1 results take?
Results typically take a few days to a week, depending on the laboratory.
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What do abnormal IGF-1 results mean, and what happens next?
High or low IGF-1 levels can suggest a growth hormone abnormality, but results are always interpreted alongside your symptoms, age, and sometimes further specialist tests, such as dynamic growth hormone testing, before a diagnosis is reached. This should be discussed with an endocrinologist or your doctor.
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Is the IGF-1 test accurate and reliable?
IGF-1 is considered a reliable marker of average growth hormone activity because it remains more stable through the day than growth hormone itself, though results can still be affected by factors such as nutrition, liver function, and other illnesses, which your doctor will take into account.
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How much does private IGF-1 testing cost, and is it on the NHS?
It is available on the NHS when clinically indicated, usually through an endocrinology referral. Private clinics also offer this test, often with faster access to specialist interpretation; cost varies by provider.
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How do I book an IGF-1 test privately, and how quickly can I be seen?
Private endocrinology clinics can typically arrange testing and a specialist consultation within a week or two.
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Will I need further tests if my IGF-1 is abnormal?
Possibly; abnormal IGF-1 results often lead to additional specialist testing, such as an oral glucose tolerance test with growth hormone measurement, or imaging of the pituitary gland, depending on the suspected cause.