An IGF-1 blood test measures how much insulin-like growth factor 1 is circulating in your bloodstream, and it is the most common way doctors check whether your body is making the right amount of growth hormone. Because growth hormone itself rises and falls in bursts all day long, a single measurement of it tells you very little. IGF-1 is far steadier, so one ordinary blood draw gives a reliable picture of growth hormone activity over the previous hours and days. In this article you will learn what the test measures, why a doctor orders it, how reference ranges are built and why they differ from one laboratory to the next, what a high or a low result can point to, and which everyday factors can nudge your number in either direction before any disease is involved.
What an IGF-1 blood test measures
Insulin-like growth factor 1 is a hormone made mostly by your liver. Your pituitary gland, a pea-sized structure at the base of the brain, releases growth hormone; growth hormone then travels to the liver and instructs it to produce IGF-1. Almost all of the growth-promoting work attributed to growth hormone is actually carried out by IGF-1 at the level of your tissues: it tells bone, muscle and cartilage cells to divide, to take up nutrients and to stay alive rather than shut down.
The test itself is a simple measurement of the concentration of that hormone in serum, the liquid part of blood left after clotting. It does not measure growth hormone directly and it does not tell you where a problem originates. It tells you whether the growth hormone system as a whole is running fast, slow, or at the pace expected for someone your age.
Why doctors measure IGF-1 instead of growth hormone
Growth hormone is released in pulses, mostly at night and after exercise. Between pulses its blood level can fall close to zero in a perfectly healthy person, which makes a random growth hormone measurement almost impossible to interpret. IGF-1 behaves differently. It circulates bound to carrier proteins that protect it from being broken down, so its level stays relatively flat across the day. That stability is the whole reason the test exists.
The main carrier protein has its own test, and clinicians sometimes order the two together when a result is ambiguous. You can read more about that companion marker in our IGFBP-3 blood test guide.
What IGF-1 does in the body
In childhood and adolescence, IGF-1 drives linear growth: it is the signal that lengthens bones at the growth plates. After the growth plates close, the hormone shifts roles. In adults it supports muscle maintenance, bone remodeling, wound repair and metabolism. It also overlaps with insulin signaling, which is why IGF-1 levels can move alongside markers of blood sugar control such as the ones covered in our fasting glucose test guide.
Why your doctor may order an IGF-1 blood test
An IGF-1 test is rarely part of a routine annual panel. It is ordered when something in your symptoms, your growth pattern or your imaging raises a specific question about growth hormone.
Common reasons in adults
In adults the test is usually requested to investigate suspected excess growth hormone, which produces a condition called acromegaly. Typical triggers include rings and shoes that no longer fit, a jaw or brow that has visibly changed shape, new joint pain, thickened skin, heavy sweating, headaches or newly diagnosed sleep apnea. The test is also used in the opposite direction, to look for adult growth hormone deficiency after pituitary surgery, radiation or a head injury, and to monitor treatment once a pituitary condition has been diagnosed. Because pituitary disorders often disturb more than one hormone, doctors frequently pair the request with a prolactin blood level guide style workup and a check of adrenal output described in our cortisol blood test guide.
Common reasons in children and teenagers
In pediatrics the question is almost always about growth. A child whose height has fallen away from their expected curve, who has delayed puberty, or who is growing unusually fast may have an IGF-1 test as part of the assessment. Since thyroid problems slow growth in a way that can look similar, a thyroid check using the markers explained in our TSH blood test results guide is often ordered at the same time.
How the test is done and how to prepare
The test needs a single ordinary blood sample, usually drawn from a vein in your arm. It takes a couple of minutes and needs no special equipment.
Before the blood draw
Many laboratories ask for an overnight fast of roughly eight hours, mainly because IGF-1 is often drawn together with glucose or insulin measurements that do require fasting. Ask the ordering clinic rather than assuming. Tell whoever takes the sample about every medication and supplement you use: estrogen taken by mouth, corticosteroids, thyroid medication and growth hormone products all influence the result. If you have been acutely ill, severely underfed or on a very low calorie diet in the preceding weeks, mention that too, because IGF-1 falls quickly in those situations.
What the report looks like
Your result appears as a number in nanograms per milliliter or micrograms per liter, next to a reference range for your age and sometimes your sex. Many laboratories also print a standard deviation score, often written as SDS or z-score, which expresses how far your value sits from the average for people your age. A score near zero is average; a score around plus or minus two sits at the edge of the usual range. That standardized score is generally more useful than the raw number, because it already accounts for age.
Normal IGF-1 levels by age
There is no single normal IGF-1 value that applies to everyone. Levels are low in early childhood, climb steeply through puberty, peak in the mid to late teens, then decline gradually across adult life. A value that is entirely healthy for a 16-year-old would be strikingly high for a 60-year-old, and the reverse is equally true. This is why comparing your number to a friend’s, or to a figure found online, tells you nothing useful.
| Life stage | Typical IGF-1 pattern | What it means for interpretation |
|---|---|---|
| Infancy and early childhood | Lowest values of the whole lifespan | Small absolute numbers are expected; growth velocity matters more than the value alone |
| Mid childhood | Slow, steady rise | Results are read against tight age bands, so an accurate date of birth is essential |
| Puberty and adolescence | Sharp peak, the highest of life | Pubertal stage, not just age, shapes the expected range |
| Young adulthood | Falls back from the adolescent peak | A value still at teenage levels in a 25-year-old deserves a second look |
| Middle age | Continues a gradual decline | Mild decline is normal aging, not a hormone disorder by itself |
| Older adulthood | Lowest adult values | A borderline low result is common and rarely meaningful on its own |
Why normal depends on the laboratory
Different laboratories use different measuring methods, and those methods do not always agree with one another. A sample that reads as slightly high on one analyzer can read as normal on another. Reference ranges are also built from different reference populations, which shifts the boundaries again. The practical consequence is simple: always compare your result to the range printed on your own report, and if you are being monitored over time, try to have repeat tests run by the same laboratory.
Reading the reference range on your report
A result just outside the printed range is not automatically abnormal. Reference ranges are usually built so that a small percentage of perfectly healthy people fall outside them. Clinicians look at how far outside, whether the pattern fits your symptoms, and what other results show. A number that sits far above the top of the range, in someone with the physical changes of acromegaly, carries very different weight from a value one point over the line in someone who feels entirely well.
What high IGF-1 levels can mean
A genuinely elevated IGF-1 result means the growth hormone system is overactive. The reasons fall into two groups.
Acromegaly and gigantism
The classic cause is a benign tumor of the pituitary gland that secretes growth hormone continuously. In adults, whose growth plates have closed, the result is acromegaly: bones thicken rather than lengthen, so hands, feet, jaw and brow enlarge slowly over years. In children and adolescents, whose growth plates are still open, the same problem produces gigantism and unusually rapid height gain. According to the National Institute of Diabetes and Digestive and Kidney Diseases, acromegaly is rare and typically appears in middle age, and because it develops so gradually it is frequently recognized late. A raised IGF-1 is usually the first laboratory clue; confirmation normally requires an oral glucose tolerance test, in which growth hormone should fall after a sugary drink and fails to do so, followed by pituitary imaging.
Other reasons for a high result
Not every high IGF-1 comes from a tumor. Adolescence itself produces very high values. Pregnancy raises IGF-1. So does use of growth hormone or of IGF-1 preparations, whether prescribed or not. Poorly controlled diabetes and kidney disease can also distort the measurement, which is one reason clinicians look at kidney function alongside the result using markers such as those in our creatinine blood test guide.
What low IGF-1 levels can mean
Low IGF-1 is a much less specific finding than high IGF-1, and it is far more often explained by something other than a pituitary problem.
Growth hormone deficiency
In children, persistently low IGF-1 together with slow growth raises the question of growth hormone deficiency, which is confirmed with stimulation testing rather than with IGF-1 alone. In adults, deficiency usually follows damage to the pituitary from a tumor, surgery, radiation or serious head trauma. Symptoms are vague on their own: fatigue, reduced muscle mass, more body fat around the waist, low mood and thinning bone. A normal IGF-1 does not rule adult deficiency out, which is why the test is a starting point and not a verdict.
Nutritional, liver, kidney and thyroid causes
Because the liver manufactures IGF-1, anything that limits liver capacity or the raw materials it needs will lower the number. Undernutrition, restrictive dieting, eating disorders, malabsorption, chronic liver disease, advanced kidney disease, poorly controlled diabetes, untreated hypothyroidism and any severe acute illness all push IGF-1 down. Low protein status is a common contributor, and clinicians often review it alongside the values explained in our albumin blood test guide. Where blood sugar handling is part of the picture, results are often read next to the insulin sensitivity estimate described in our HOMA-IR blood results guide and the broader context set out in our diabetes symptoms and treatments guide.
What can shift your IGF-1 result
Before concluding that a result reflects disease, clinicians run through the ordinary influences that move IGF-1 in healthy people. The table below groups the most common ones.
| Influence | Usual direction | Why it happens |
|---|---|---|
| Age | Peaks in adolescence, then falls | Growth hormone output declines steadily after early adulthood |
| Undernutrition or crash dieting | Lower | The liver reduces IGF-1 output when energy and protein are scarce |
| Chronic liver disease | Lower | A damaged liver cannot manufacture the hormone efficiently |
| Untreated hypothyroidism | Lower | Thyroid hormone is needed for normal growth hormone signaling |
| Estrogen taken by mouth | Lower | Oral estrogen passes through the liver and blunts IGF-1 production |
| Pregnancy | Higher | The placenta produces its own growth-hormone-like signal |
| Growth hormone products | Higher | Extra growth hormone directly drives liver IGF-1 output |
| Laboratory method | Either direction | Different analyzers and reference populations shift the boundaries |
Bone health is closely tied to the same hormonal system, so an abnormal IGF-1 is often reviewed together with the bone-turnover information found in our alkaline phosphatase results guide.
When to see a doctor
Book an appointment rather than waiting for the next routine check-up if you notice a gradual change in the size of your hands, feet, ring size or shoe size in adulthood; a visible change in the shape of your jaw, brow or facial features over a few years; new gaps opening between your teeth; persistent headaches combined with a change in vision, particularly a loss of side vision; heavy sweating and thickening skin without an obvious cause; or new joint pain with carpal tunnel symptoms.
For a child, ask for an assessment if height has drifted away from the growth curve over two or more visits, if growth has become unusually rapid, or if puberty is clearly early or clearly delayed. Seek prompt medical advice if a headache becomes sudden and severe or vision changes abruptly, as pituitary problems can occasionally present as an emergency. Do not start, stop or adjust any hormone treatment because of a single laboratory number; interpretation belongs with the clinician who knows your history. If your results are being tracked alongside sex hormone levels, the context in our insulin blood test guide can help you follow the metabolic side of the same conversation.
Latest scientific advances
Research over the past three years has focused less on discovering new uses for the IGF-1 test and more on making the existing test more trustworthy. That is quietly good news for anyone trying to understand a borderline result.
A 2026 review of the biochemical diagnosis of acromegaly, published in Vitamins and Hormones, concluded that IGF-1 remains the cornerstone measurement because it reflects growth hormone output in a stable, integrated way. The same review noted that growth hormone and IGF-1 results disagree with one another in a substantial minority of patients, and that obesity, diabetes, liver disease and kidney disease are among the reasons why. What this means for you: if your IGF-1 and growth hormone results seem to tell different stories, that is a recognized clinical situation rather than a laboratory error, and it is why doctors add an oral glucose tolerance test — a test in which you drink a measured sugary solution and hormone levels are followed afterwards — instead of relying on one number.
A detailed review of IGF-1 testing published in Critical Reviews in Clinical Laboratory Sciences examined why the same sample can produce different answers in different laboratories. The authors described interference from the binding proteins that carry IGF-1 in the blood, differences between commercial test kits, and the difficulty of building reference intervals that work everywhere. They highlighted mass spectrometry — a technique that identifies a molecule by weighing it very precisely rather than by capturing it with an antibody — as a route to more consistent results. What this means for you: comparing a value measured at one laboratory with a range published by another is genuinely unreliable, and repeat testing is best done in the same place.
A 2025 cross-sectional study of healthy young men in Korea, published in Translational and Clinical Pharmacology, built local reference ranges for IGF-1 and its main binding protein and found that values varied noticeably across seasons of the year. The study looked at one population and one measuring method, so it should be read as a signal rather than a settled fact. What this means for you: modest movement between two tests taken months apart does not automatically indicate that anything has changed in your health.
Finally, a 2025 review in Expert Review of Endocrinology and Metabolism argued that acromegaly is still under-diagnosed and usually identified only once the disease is advanced, because early physical changes are subtle and easy to attribute to normal aging. It restated that measuring IGF-1 is the first step once the condition is suspected, and that growth hormone and IGF-1 should always be interpreted together. What this means for you: raising a slow physical change with your doctor is worthwhile even when it seems minor, since the test that follows is straightforward.
Glossary
| Term | Definition |
|---|---|
| IGF-1 | Insulin-like growth factor 1, a hormone made mainly by the liver in response to growth hormone. It carries out most of growth hormone’s effects on tissues. |
| Growth hormone | A hormone released in pulses by the pituitary gland. It drives growth in childhood and helps maintain muscle, bone and metabolism in adults. |
| Pituitary gland | A pea-sized gland at the base of the brain that controls several hormone systems, including growth hormone release. |
| Acromegaly | A condition caused by long-term excess growth hormone in adults, leading to gradual enlargement of the hands, feet and facial bones. |
| Gigantism | Excess growth hormone that begins in childhood, before the growth plates close, producing unusually rapid increases in height. |
| IGFBP-3 | Insulin-like growth factor binding protein 3, the main carrier protein that transports IGF-1 in the blood and protects it from breakdown. |
| Reference range | The span of values expected in a healthy population of a given age and sex, printed on your laboratory report next to your result. |
| Standard deviation score | Also written SDS or z-score, a figure showing how far your value sits from the average for your age. Zero is average. |
| Oral glucose tolerance test | A test in which you drink a measured sugary solution and blood is sampled afterwards to see how a hormone responds. |
| Growth plate | The zone of growing cartilage near the ends of a child’s long bones. Once it closes after puberty, height stops increasing. |
Frequently asked questions
Do I need to fast before an IGF-1 blood test?
Requirements differ between laboratories. IGF-1 itself is not strongly affected by a recent meal, but it is often drawn together with glucose or insulin measurements that do require fasting, so many clinics ask for an overnight fast of about eight hours. Water is normally allowed. The safest approach is to call the clinic or read the instructions on your test order rather than guessing, because arriving unfasted when fasting was required can mean rebooking the appointment. Continue your regular medications unless your doctor has told you otherwise, and mention every product you take when you arrive.
What is a normal IGF-1 level for my age?
There is no universal figure. Values are low in early childhood, peak during puberty, and decline gradually through adult life, so each laboratory prints an age-specific and often sex-specific range next to your result. Those ranges also differ between laboratories because measuring methods and reference populations differ. Use the range on your own report as the reference point, and if a standard deviation score is provided, treat it as the more informative number, since it already adjusts for your age.
How much does an IGF-1 blood test cost?
Prices vary widely by country, laboratory and whether the test is ordered by a physician or bought directly. When a doctor orders it to investigate a specific symptom or to monitor a known pituitary condition, health insurance commonly covers it, though coverage rules differ between plans. Direct-to-consumer testing is generally paid out of pocket. Ask the laboratory for the price before the draw, and ask your insurer whether a physician’s order changes what you pay.
Can exercise or diet change my IGF-1 level?
Yes, though usually within the normal range rather than beyond it. Sustained undernutrition, very low calorie diets and inadequate protein intake lower IGF-1 noticeably, because the liver needs both energy and building blocks to produce it. Regular resistance training and adequate protein support normal levels. A single workout or a single meal will not meaningfully move your result. Extreme measures aimed at pushing IGF-1 up or down are not advisable, since both very high and very low levels are associated with health problems.
Does a high IGF-1 result mean I have a tumor?
Not on its own. A high result raises the question and prompts further testing, but adolescence, pregnancy, use of growth hormone products, and some laboratory method differences all produce elevated values without any tumor being present. Confirming acromegaly requires more than one abnormal number: doctors typically add an oral glucose tolerance test and, if that is also abnormal, imaging of the pituitary gland. Try not to draw conclusions from a single figure before that process is complete.
What is the difference between an IGF-1 test and a growth hormone test?
A growth hormone test measures the hormone released directly by the pituitary gland, which comes in pulses and can be near zero in a healthy person between bursts. That makes a single random measurement hard to interpret. An IGF-1 test measures a downstream hormone made by the liver in response to growth hormone, and its level stays much more stable through the day. In practice, IGF-1 is used for screening and monitoring, while growth hormone is measured under controlled conditions such as suppression or stimulation testing.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases — Acromegaly — NIDDK Health Information, reviewed 2025 — niddk.nih.gov
- MedlinePlus, National Library of Medicine — Growth Hormone Tests — MedlinePlus Medical Test, reviewed 2025 — medlineplus.gov
- Cleveland Clinic — Acromegaly — Cleveland Clinic Health Library, reviewed 2025 — my.clevelandclinic.org
- Mayo Clinic — Acromegaly: Diagnosis and Treatment — Mayo Clinic Diseases and Conditions, reviewed 2025 — mayoclinic.org
- Cardoso LM, Silva G, Jesus B, Monsanto A, Vinagre J, Gomes L — Acromegaly: Biochemical diagnosis — Vitamins and Hormones, 2026 — doi.org/10.1016/bs.vh.2026.01.002
- Huang R, Shi J, Wei R, Li J — Challenges of insulin-like growth factor-1 testing — Critical Reviews in Clinical Laboratory Sciences, 2024 — doi.org/10.1080/10408363.2024.2306804
- Jung SM, Lee SH, Lee H, Kim EN, Bae KS — Serum IGF-1 and IGFBP-3 levels in healthy Korean men aged 19-40 years: a cross-sectional analysis of reference ranges and seasonal variation — Translational and Clinical Pharmacology, 2025 — doi.org/10.12793/tcp.2025.33.e13
- Freda PU — Acromegaly: diagnostic challenges and individualized treatment — Expert Review of Endocrinology and Metabolism, 2025 — doi.org/10.1080/17446651.2024.2448784
Further reading
- Explore the hormone that shapes muscle mass and bone density by reading our testosterone blood levels guide.
- Review the marker that tracks reproductive hormone balance with our estradiol blood test results guide.
- Check the nutrient that underpins calcium absorption and bone strength in our vitamin D blood levels guide.
- Understand how weakened bone develops and is managed by reading our osteoporosis symptoms and treatments guide.
- Examine the gland that fine-tunes calcium in your blood with our parathyroid hormone levels guide.
Understand your lab results with BloodSense
An IGF-1 result rarely stands alone. It is usually read alongside growth hormone, the binding protein IGFBP-3, thyroid and blood sugar markers, and measures of liver and kidney function, and each of those has its own age-adjusted range. BloodSense turns that cluster of numbers into plain-language explanations so you can see how your values fit together and arrive at your appointment with better questions. It helps you understand your results; it does not diagnose conditions and it does not replace your doctor.
