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An IGF-1 blood test measures insulin-like growth factor 1, a hormone your liver releases in response to growth hormone. Because growth hormone comes out in short bursts throughout the day, a single reading of it tells you very little. IGF-1 stays far steadier, so a one-off blood sample gives clinicians a reliable window onto how much growth hormone your body is actually producing. That is why the test exists, and why it sits at the centre of investigating conditions such as acromegaly and growth hormone deficiency.
People usually end up looking into this test for one of two reasons. Either a doctor has raised the possibility of a growth hormone problem and ordered it, or someone already has a result in front of them — a number, an age-adjusted range, maybe a “high” or “low” flag — and wants to understand what it means before their next appointment.
This guide covers both. It explains what the test measures, why normal IGF-1 ranges shift so dramatically with age, what high and low results can point to, the symptoms sometimes linked to each, and the practical side of arranging an IGF-1 blood test privately in the UK — including cost, home testing and how private testing compares with the NHS. Throughout, the emphasis is on interpretation in context, because an IGF-1 figure on its own rarely settles anything.
Insulin-like growth factor 1 (IGF-1), historically called somatomedin C, is a protein hormone that closely resembles insulin in structure. It’s produced mainly by the liver, though muscle and other tissues make it too, and it’s released when growth hormone (GH) from the pituitary gland reaches the liver and switches on production.
IGF-1 does much of growth hormone’s practical work. In childhood and adolescence it drives the lengthening of bones and the growth of tissue; in adults it keeps up an anabolic role, supporting muscle and bone maintenance and playing a part in how the body handles glucose and fats. In effect, growth hormone gives the instruction and IGF-1 carries a large share of it out.
One quirk makes IGF-1 particularly useful in the lab. Growth hormone is secreted in pulses and its blood level swings wildly from hour to hour, so a single GH measurement is hard to interpret. IGF-1 changes very little across the day. Measuring it therefore gives a far more stable picture of average growth hormone activity than trying to catch GH itself at the right moment.
The test measures the total concentration of IGF-1 circulating in your blood, usually reported in nanomoles per litre (nmol/L) by UK laboratories, or in nanograms per millilitre (ng/mL), which many international sources and some private labs use.
Because IGF-1 mirrors growth hormone activity, the result is used as an indirect marker of whether the growth hormone axis is running normally, too high, or too low. Clinicians typically request it to help investigate:
IGF-1 is sometimes measured alongside IGFBP-3 (insulin-like growth factor binding protein 3), the main protein that carries IGF-1 in the blood. Because IGFBP-3 levels tend to move in step with IGF-1, it can add useful context when investigating growth hormone disorders — though the standard IGF-1 blood test on its own remains the usual starting point.
It’s worth being clear about what the test doesn’t do. A single IGF-1 result doesn’t diagnose any of these conditions by itself. As Lab Tests Online UK explains, it’s used to assess growth hormone activity and evaluate pituitary function — a screening and monitoring tool that points clinicians toward further investigation when a result sits outside the expected range for someone’s age and sex.
This is the question most people arrive with, and the honest answer is that there is no single normal IGF-1 number that applies to everyone. A level that’s completely healthy for a 17-year-old would be strikingly high for a 60-year-old. Any meaningful “normal” has to be tied to age, and usually sex as well.
IGF-1 follows a clear lifelong arc: it’s relatively low in early childhood, rises steadily through childhood, peaks sharply around puberty, and then declines gradually across adult life. By your fifties, a typical IGF-1 level is roughly half what it was in your late teens. This is normal, expected ageing — not a problem to be corrected. That decline is also why normal IGF-1 levels for adults can’t be pinned to one figure: the healthy window keeps moving down the older you get.
That’s why laboratories don’t hand you a single cut-off. They compare your result against an age-banded (and often sex-specific) reference range, and increasingly express it as a Z-score or standard deviation score (SDS), which we come to below.
The table below works as an IGF-1 levels-by-age chart, showing widely cited adult reference intervals published by the University of Rochester Medical Center, in ng/mL. They’re useful for understanding the shape of the age relationship — how much the range shifts as you get older — rather than as a definitive yardstick for your own result.
| Age band | Typical IGF-1 reference range (ng/mL) |
|---|---|
| 16–24 years | 182 – 780 |
| 25–39 years | 114 – 492 |
| 40–54 years | 90 – 360 |
| 55 years and older | 71 – 290 |
Source: University of Rochester Medical Center Health Encyclopedia. Ranges are illustrative and assay-dependent — always interpret your result against the reference range printed on your own report.
Two points matter more than the numbers themselves. First, the steep downward drift across the bands shows exactly why age adjustment is non-negotiable. Second, these are ng/mL figures from a US source; UK reports frequently express the IGF-1 normal range in nmol/L instead.
Because of that, don’t try to read a UK nmol/L result against a ng/mL chart directly — the two units use different scales, and converting between them requires the specific conversion factor for the assay your laboratory used. If your report is in nmol/L, the reliable comparison is the nmol/L reference range printed alongside it, not a ng/mL table found online. When in doubt, ask the laboratory or clinician which units your result uses and what the matching range is.
If you compared two IGF-1 reports from different labs, you might find the “normal” range printed on each doesn’t match — and neither is wrong. Reference intervals vary because of:
The practical takeaway: the reference range on your report, from your laboratory, is the one that counts. A result copied from a chart online — or from a friend’s report run by a different lab — can be genuinely misleading.
Because a raw IGF-1 number means little without its age context, many UK labs report an IGF-1 Z-score (also called an SDS, or standard deviation score) alongside it. This expresses how far your result sits from the average for your age and sex, measured in standard deviations.
The Z-score is often more informative than the raw number precisely because it has already done the age-and-sex maths for you. If your report includes one, it’s usually the figure worth focusing on when you talk it through with a clinician.
A high IGF-1 result generally suggests your body may be producing too much growth hormone — but “may be” is doing important work in that sentence. Elevated IGF-1 is a signal to look further, not a diagnosis in itself.
The condition most associated with genuinely high IGF-1 in adults is acromegaly, usually caused by a benign (non-cancerous) tumour on the pituitary gland that drives excess growth hormone. In children and adolescents, before the growth plates fuse, the same excess causes gigantism. IGF-1 is the recommended first-line screening test when acromegaly is suspected, and UK NHS laboratories such as North Bristol NHS Trust describe it as the preferred initial test for that purpose.
Crucially, a raised IGF-1 doesn’t confirm acromegaly on its own. Other factors can push levels up, and results occasionally come back high without any underlying growth hormone disorder — sometimes as a false positive related to the assay. There’s also no single universal number that counts as “dangerously high,” because what’s elevated depends entirely on your age- and sex-adjusted range; a value normal for a teenager could be clearly raised for someone in their fifties. That’s why diagnosis doesn’t stop at the blood test.
If IGF-1 comes back elevated and acromegaly is suspected, the standard confirmatory step is an oral glucose tolerance test (OGTT). As set out in the NIH StatPearls review of acromegaly, a healthy person’s growth hormone suppresses after a 75g glucose load, whereas in acromegaly GH fails to suppress properly. Imaging of the pituitary gland, usually an MRI, is then used to locate any tumour. Recent international consensus guidance also allows that, in someone with typical clinical features, an IGF-1 well above the upper limit of normal for their age can itself be considered confirmatory — but this is a specialist judgement, not something to conclude from a home result.
The message for anyone reading a high result at home: it warrants a proper clinical review, and it is not the same thing as a confirmed diagnosis.
The symptoms linked to growth hormone excess develop slowly, often over years, which is part of why acromegaly is frequently diagnosed late. Features that may accompany persistently high IGF-1 include:
None of these is specific to high IGF-1 — each has many other explanations — and many people with a mildly raised result have no symptoms at all. Symptoms are a reason to seek assessment, not a self-diagnosis.
Beyond acromegaly and gigantism, IGF-1 can be raised or falsely elevated by a range of factors, including:
Because so much can influence the figure, a high result is always interpreted alongside symptoms, clinical history and confirmatory testing rather than in isolation.
A low IGF-1 result suggests reduced growth hormone activity — but, as with high results, a single low value is a starting point rather than an answer. IGF-1 is only an initial screening tool for growth hormone deficiency, and one low reading is not diagnostic on its own.
In adults, low IGF-1 can be associated with growth hormone deficiency, which may follow pituitary disease, pituitary surgery, radiotherapy or significant head injury. In children, a low level may be relevant when growth is slower than expected, though a single result never confirms deficiency and always needs specialist assessment. It’s also worth knowing that a meaningful number of people with genuine growth hormone deficiency have IGF-1 levels within the normal range — which is exactly why clinicians don’t rely on IGF-1 alone.
In adults, the features sometimes linked to low growth hormone activity are notably non-specific and overlap with many common conditions:
In children, the more relevant signs relate to growth: a slower-than-expected growth rate and shorter stature compared with peers.
Because these adult symptoms are so easily caused by other things — from thyroid problems to sleep, stress and nutrition — they’re never enough to point to low IGF-1 by themselves. If they resonate, our best blood tests for fatigue guide walks through the broader panel of markers usually worth checking first.
Low IGF-1 has a wide range of possible contributors, and many have nothing to do with the pituitary gland:
Because nutrition, liver and thyroid function all feed into the result, a low IGF-1 usually prompts a wider look rather than an immediate leap to growth hormone deficiency.
It’s easy to assume IGF-1 and growth hormone are interchangeable, but they play different roles, and understanding the relationship explains why the test is done the way it is.
Growth hormone is made by the pituitary gland and released into the blood in irregular pulses. When it reaches the liver, it triggers the production of IGF-1, which then carries out many of growth hormone’s downstream effects on bone, muscle and tissue. So growth hormone is the signal, and IGF-1 is a major part of the response.
The practical difference is stability. Growth hormone levels swing so much from hour to hour that a random GH blood test is difficult to interpret. As MedlinePlus notes, IGF-1 stays far steadier, so it acts as a dependable summary of average growth hormone activity. That’s the whole reason clinicians usually measure IGF-1 first rather than chasing growth hormone directly — and why growth hormone testing, when it’s needed, tends to involve dynamic tests like suppression or stimulation rather than a single sample.
(Note that IGF-1 testing is distinct from an IGF-1 generation test, a specialist procedure that involves administering growth hormone and then measuring the IGF-1 response to assess growth hormone resistance. That’s a different investigation from the standard blood test described here.)
The test itself is straightforward. A healthcare professional takes a blood sample from a vein in your arm, and the sample is sent to a laboratory that measures your IGF-1 concentration and compares it against the age- and sex-adjusted reference range.
There’s no complex preparation for a standalone IGF-1 test. The main thing worth flagging to whoever arranges your test is any high-dose biotin supplement you take, as biotin can interfere with some laboratory assays; you may be advised to pause it for a few days beforehand. Otherwise the sample can generally be taken at a convenient time.
For a standalone IGF-1 test, fasting is not generally required. IGF-1 levels don’t fluctuate with meals the way glucose or triglycerides do, so eating beforehand doesn’t meaningfully change the result.
There are two sensible caveats. First, if your IGF-1 is being taken as part of a wider panel — a metabolic or hormone profile that includes markers such as glucose or a lipid panel — those other tests may require fasting, so you’d follow the fasting instruction for the panel as a whole. Second, prolonged fasting or significant undernutrition genuinely lowers IGF-1, so an extreme fast in the run-up to testing could pull the result down. For a normal, standalone test, though, you can eat as usual unless told otherwise. Always follow the specific instructions given by the provider arranging your test.
IGF-1 is measured from a venous blood sample — blood drawn from a vein in your arm by a trained phlebotomist — rather than a simple finger-prick, so it isn’t a test you can reliably self-collect from a postal kit. What “at home” realistically means for this test is a home-visit arrangement, where a phlebotomist comes to you to take the sample, which is then sent to the laboratory in the usual way.
Whether a home visit is available, and where, depends on the provider. At Swift Blood Tests, IGF-1 is offered within our Metabolic Hormones (Cortisol, Insulin, IGF-1) Blood Test, and you can check the current sampling and appointment options — including any clinic or home-visit arrangements in your area — when you book. [CONFIRM WHETHER SWIFT OFFERS HOME-VISIT PHLEBOTOMY FOR THIS TEST AND EDIT THIS SENTENCE ACCORDINGLY.]
Private IGF-1 testing costs vary between providers, and the price often depends on how the test is arranged — a standalone IGF-1 test, IGF-1 within a wider hormone panel, and clinic versus home-visit sampling can all sit at different price points.
The current price for IGF-1 testing at Swift Blood Tests is £185.00 . Because pricing and panel options can change, the most reliable figure is always the one shown on the live service page, which reflects the current cost and exactly what’s included. We’d suggest checking there before booking rather than relying on prices quoted elsewhere, which date quickly.
On the NHS, IGF-1 is typically measured when there’s a clinical reason to investigate the growth hormone axis — for example, when a doctor is looking into possible acromegaly or growth hormone deficiency — and testing is arranged through your GP or a specialist as part of that assessment.
Private testing works differently in one practical respect: you can usually arrange an IGF-1 blood test directly, without waiting for a referral, and choose a time and location that suits you. That convenience is the main reason people opt for it — whether to look into symptoms sooner, to monitor a known situation, or simply to avoid a wait. The trade-off is that a private result still needs interpreting in context, ideally with a clinician, exactly as an NHS result would be. Neither route changes what the number means; they differ mainly in how you access the test.
Turnaround varies by laboratory and by how the test is arranged, so the most reliable answer comes from the provider handling your sample. IGF-1 is a routine laboratory analyte rather than an exotic one, and results are generally available within a few working days. At Swift Blood Tests, the expected turnaround for this test is 3 days; the current timescale is confirmed on the service page when you book.
When your result comes back, it’s most useful to read it in three parts: your value, the reference range printed beside it, and — if provided — your Z-score. Broadly:
Whatever the number, the same principle holds: an IGF-1 result is one piece of information, interpreted by a clinician alongside your symptoms, history and — where needed — additional tests. A borderline result just outside the range is often not a problem at all and needs professional review rather than alarm. If you’d like a broader primer on reading lab reports, our guide on blood test results explained covers how reference ranges and flags work in general.
An IGF-1 result — particularly one flagged high or low — is a reason to have a conversation with a healthcare professional rather than to draw conclusions alone. It’s worth seeking review if your result sits outside the reference range for your age, if you have symptoms that prompted the test in the first place, or if you’re simply unsure what the number means in your situation.
A clinician can put the figure in context, decide whether repeat or confirmatory testing is appropriate, and consider the other factors — nutrition, thyroid, liver, medications — that shape IGF-1. This is medical information to support that conversation, not a substitute for individual assessment, and it isn’t a basis for self-diagnosis or for starting or stopping any treatment.
You don’t necessarily need to go through your GP to have IGF-1 measured. Private blood testing lets you arrange the test directly, with a venous sample taken by a trained phlebotomist and analysed by an accredited laboratory, and results returned to you with the reference range for interpretation.
People choose private testing for different reasons — wanting to investigate symptoms without delay, monitoring a known situation, or simply preferring the convenience of booking around their own schedule. If that’s you, you can order IGF-1 directly through our Metabolic Hormones (Cortisol, Insulin, IGF-1) Blood Test, which measures IGF-1 alongside related markers, and arrange your appointment through online booking.
Whichever route you take, the value of the test lies in interpreting the result properly — against the right age-adjusted range, in the context of your symptoms and history, and with a clinician where the result calls for it.
What is a normal IGF-1 level? There’s no single normal figure. Normal IGF-1 depends heavily on age and sex, and is highest around puberty before declining through adult life. Your result should be compared against the age-adjusted reference range printed on your own report, ideally alongside a Z-score.
What is considered a high IGF-1 level? There isn’t one universal cut-off. Because the healthy range falls with age, a level that’s normal for a teenager can be clearly raised for an older adult. A result is treated as high when it sits above the upper limit of your own age- and sex-adjusted reference range, and even then it’s interpreted alongside symptoms and, where needed, confirmatory testing rather than on its own.
Is IGF-1 high in acromegaly? Yes — acromegaly is driven by excess growth hormone, which raises IGF-1, and IGF-1 is the recommended first-line screening test when acromegaly is suspected. But a high IGF-1 doesn’t confirm acromegaly by itself; diagnosis is confirmed with further tests such as an oral glucose tolerance test and pituitary imaging.
Is low IGF-1 associated with growth hormone deficiency? It can be. Low IGF-1 may point to reduced growth hormone activity, but it’s only a screening finding — nutrition, liver disease, an underactive thyroid, chronic illness and ageing can all lower IGF-1, and some people with genuine deficiency have normal IGF-1. A low result needs assessment in context rather than being taken as a diagnosis on its own.
Do you need to fast for an IGF-1 blood test? Not for a standalone IGF-1 test — meals don’t meaningfully affect the result. You may need to fast if IGF-1 is bundled into a wider panel that includes tests such as glucose. Follow the instructions your provider gives you.
Can you get an IGF-1 blood test at home? IGF-1 needs a venous blood sample, so it isn’t suited to a self-collected finger-prick kit. Where “at home” is possible, it usually means a home-visit phlebotomist taking the sample. Availability depends on the provider, so check the sampling options when you book.
How much does an IGF-1 blood test cost in the UK? Private prices vary and depend on whether IGF-1 is tested on its own or within a wider panel, and on how the sample is collected. For the current cost at Swift Blood Tests, see the live service page.
Is IGF-1 the same as growth hormone? No. Growth hormone is released by the pituitary in pulses; IGF-1 is produced by the liver in response and carries out much of growth hormone’s work. Because IGF-1 stays stable through the day while growth hormone swings, IGF-1 is used as a reliable marker of average growth hormone activity.
How long do IGF-1 results take? This depends on the laboratory and how the test is arranged. IGF-1 is a routine analyte and results are usually available within a few working days — your provider can confirm the exact timescale.
Community discussion: People often compare their own IGF-1 results and reference ranges in patient communities such as r/acromegaly on Reddit. These threads can be reassuring or useful for context, but they are personal experiences rather than medical advice, and lab ranges differ between individuals and laboratories — your own report and a clinician remain the reliable guide.
This article is for general information and education. It is not a diagnosis and is not a substitute for advice from a qualified healthcare professional. Always interpret blood test results against the reference range provided by the testing laboratory and discuss them with a clinician.
