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Quick take
- What it measures: The IGF-1 blood test measures insulin-like growth factor 1, a hormone produced mainly by the liver in response to growth hormone.
- Why it is useful: Growth hormone rises and falls in pulses throughout the day, while IGF-1 is comparatively steadier, so IGF-1 is often used as a practical marker of overall growth-hormone activity.
- Common reasons for testing: Evaluation of possible acromegaly, gigantism, growth hormone deficiency, unexplained growth problems in children, pituitary disease, or monitoring of growth hormone treatment.
- Preparation: Most IGF-1 tests do not require fasting. Tell your clinician about biotin supplements, growth hormone or peptide use, estrogen therapy, steroids, diabetes medicines, and any recent acute illness.
- How results are interpreted: IGF-1 must be compared with age- and sex-specific reference ranges, and many labs report a z-score to show how far your result is from the expected average for your demographic group.
What is IGF-1?
Insulin-like growth factor 1, usually shortened to IGF-1, is a hormone-like protein involved in growth, tissue repair, bone development, muscle maintenance, and metabolism. It is made primarily in the liver after stimulation by growth hormone, which is released by the pituitary gland at the base of the brain. The U.S. National Library of Medicine’s MedlinePlus guide to IGF-1 testing explains that IGF-1 and growth hormone work together to support normal growth of bones and tissues.
The key reason clinicians measure IGF-1 rather than relying only on a random growth hormone blood level is stability. Growth hormone secretion is pulsatile: it can be high during one burst and very low between bursts. IGF-1 stays more stable over the day, giving clinicians a better snapshot of average growth hormone activity. This does not make IGF-1 a stand-alone diagnosis for every growth hormone disorder, but it makes the test one of the most useful first-line blood tests in pituitary and growth evaluations.
IGF-1 changes naturally over a lifetime. Levels are generally lower in early childhood, rise during puberty, and then gradually decline through adulthood. Because of this normal age pattern, a number that looks high for an older adult could be normal for an adolescent, and a number that looks low for a teenager could be expected in an older adult. That is why the reference interval printed on your own lab report matters more than any generic range found online.
What does the IGF-1 blood test measure?
The igf 1 blood test measures the concentration of IGF-1 in a blood sample, usually serum. Many laboratories also report an IGF-1 z-score, also called a standard deviation score. A z-score compares your IGF-1 level with people of similar age and sex. For example, a z-score near 0 is near the expected average, while positive values are above average and negative values are below average. Mayo Clinic Laboratories lists age-dependent IGF-1 reference intervals and reports z-scores for some IGF-1 assays, with a common interpretive interval of roughly -2.0 to +2.0 standard deviations for the z-score on its cataloged test information: Mayo Clinic Laboratories IGF-1 test catalog.
Depending on the lab, the test may be performed by immunoassay or by liquid chromatography-tandem mass spectrometry, often abbreviated LC/MS or LC-MS/MS. Methods and reference intervals are not interchangeable. If your doctor is monitoring a long-term condition such as acromegaly or growth hormone therapy, using the same laboratory or at least the same method over time can make trends easier to interpret.
Why not just test growth hormone?
A random growth hormone level can be misleading because growth hormone is secreted in bursts. A single blood draw may catch a peak, a trough, or something in between. IGF-1 is more stable and better reflects integrated growth hormone activity over time. For suspected growth hormone deficiency or acromegaly, clinicians may still order specialized stimulation or suppression tests after the IGF-1 result.
Who may need an IGF-1 blood test?
IGF-1 testing is usually ordered when symptoms, growth patterns, medication history, or pituitary history suggest abnormal growth hormone activity. It is not a general wellness test for everyone, and an abnormal number should not be used by itself to start or change hormone treatment.
Possible reasons in children and adolescents
- Short stature or slowed growth compared with expected growth curves
- Very rapid linear growth or unusually tall stature for age and family pattern
- Delayed or abnormal puberty evaluation when growth hormone function is part of the question
- Known or suspected pituitary or hypothalamic disease
- Monitoring of prescribed growth hormone therapy
Possible reasons in adults
- Symptoms or physical changes that raise concern for acromegaly, such as enlargement of hands, feet, jaw, or facial features; increasing ring or shoe size; excessive sweating; headaches; sleep apnea; or joint pain
- History of pituitary tumor, pituitary surgery, radiation to the head or pituitary region, traumatic brain injury, or multiple pituitary hormone deficiencies
- Evaluation of possible adult growth hormone deficiency when there is a strong medical reason to suspect it
- Monitoring after treatment for acromegaly or during prescribed growth hormone replacement
For suspected acromegaly, IGF-1 is a central screening test. The Endocrine Society clinical practice guideline on acromegaly states that a normal IGF-1 level generally excludes acromegaly in most typical clinical settings, while an elevated IGF-1 should be interpreted alongside clinical findings and confirmed with additional testing when appropriate.
For suspected adult growth hormone deficiency, the picture is more nuanced. The Endocrine Society guideline on adult growth hormone deficiency notes that a normal IGF-1 does not exclude growth hormone deficiency, especially in adults with pituitary disease. ARUP Consult similarly describes IGF-1 as a useful initial test but not sufficient by itself to diagnose or rule out growth hormone deficiency: ARUP Consult: Growth Hormone Deficiency.
How to prepare for the IGF-1 blood test
Most IGF-1 blood tests are simple venous blood draws and do not require fasting. However, preparation can differ by ordering clinician and laboratory, especially when IGF-1 is being drawn as part of a larger endocrine panel. Follow the instructions on your lab order.
| Preparation question | Typical guidance | Why it matters |
|---|---|---|
| Do I need to fast? | Usually no, unless another test on the same order requires fasting. | IGF-1 is more stable than growth hormone and is not usually ordered as a fasting-only test. |
| Should I stop biotin? | Ask your clinician or lab. Many direct-access and clinical lab instructions advise avoiding biotin for about 72 hours before some hormone tests. | The FDA warns that biotin can interfere with certain lab tests that use biotin-based assay technology, causing falsely high or falsely low results depending on the test design: FDA biotin interference information. |
| Should I stop medications? | Do not stop prescribed medications unless the ordering clinician tells you to. | Growth hormone, estrogen therapy, glucocorticoids, diabetes medicines, and other treatments may be medically important and need planned interpretation rather than abrupt changes. |
| Does timing of day matter? | Usually less than it does for growth hormone. Your clinician may still prefer consistent timing for repeat monitoring. | Consistency helps when tracking trends over time. |
| Should I test while sick? | If the test is not urgent, ask whether to postpone during significant acute illness. | Acute illness, poor nutrition, and metabolic stress can affect endocrine markers and complicate interpretation. |
Before the draw, tell the person ordering the test if you take over-the-counter supplements, hair/nail products with biotin, prescribed growth hormone, testosterone or estrogen therapy, glucocorticoids such as prednisone, diabetes medications, or non-prescribed peptides sometimes marketed for growth hormone effects. Also mention pregnancy, recent major illness, liver disease, kidney disease, uncontrolled diabetes, eating disorders, or known pituitary conditions.
What happens during the blood draw?
The IGF-1 test uses a standard blood sample. A phlebotomist or other trained professional cleans the skin, places a small needle into a vein, collects blood into a tube, removes the needle, and applies pressure or a bandage. The collection itself usually takes only a few minutes.
Risks are the same as most routine blood draws: brief discomfort, bruising, lightheadedness, or rarely infection at the puncture site. If you have a history of fainting with blood draws, difficult veins, a bleeding disorder, or use blood thinners, tell the collection staff before the draw.
Turnaround time depends on the lab and whether the sample is sent to a reference laboratory. Mayo’s catalog lists report availability of several days for its IGF-1 LC/MS test, while direct-access services may quote typical turnaround windows such as 2–8 business days depending on the lab network and logistics.
How to understand IGF-1 results
Your IGF-1 result is usually reported in ng/mL, mcg/L, or nmol/L, depending on the laboratory. Do not compare results across units without a validated conversion, and do not compare your number with a range from a different lab. The most important pieces of the report are:
- Your IGF-1 value
- The reference interval for your age and sex
- The z-score or standard deviation score, if reported
- The method and lab used
- Any interpretive comments or specimen quality notes
Result patterns and what they may suggest
| Result pattern | Possible interpretation | Common next step |
|---|---|---|
| Within the reference range | Often reassuring, especially when acromegaly is the concern and the result fits the clinical picture. | Discuss whether symptoms need another explanation. If adult growth hormone deficiency is still suspected because of pituitary disease, stimulation testing may still be considered. |
| High IGF-1 | May suggest excess growth hormone activity, including acromegaly in adults or gigantism in children. Puberty, pregnancy, assay differences, and treatment effects can also influence results. | Repeat IGF-1 may be ordered, often with the same method. Clinicians may use an oral glucose growth hormone suppression test and, if biochemically confirmed, pituitary imaging. |
| Low IGF-1 | May support growth hormone deficiency in the right setting, but can also reflect malnutrition, liver disease, uncontrolled diabetes, hypothyroidism, chronic illness, or oral estrogen therapy. | Review medical context and interfering factors. If growth hormone deficiency is suspected, dynamic stimulation testing may be needed. |
| Borderline or discordant result | May occur because of lab-method differences, biologic variation, supplements, medications, or a mismatch between symptoms and labs. | Repeat testing, use the same lab method, review medications and supplements, and consider referral to endocrinology. |
High IGF-1 and acromegaly
In adults, persistently high IGF-1 can be a clue to acromegaly, most often caused by a growth hormone-secreting pituitary adenoma. Acromegaly can develop slowly, and many people notice changes only after comparing old photos, ring size, glove size, or shoe size. Other features may include headaches, carpal tunnel symptoms, joint pain, oily skin, sweating, snoring or sleep apnea, high blood pressure, and changes in glucose control.
A high IGF-1 result alone is not the whole diagnosis. The ARUP Consult acromegaly testing guide describes IGF-1, growth hormone, and oral glucose tolerance testing as part of the diagnostic approach. In many evaluations, clinicians confirm lack of growth hormone suppression after an oral glucose load before moving to pituitary MRI and treatment planning.
Low IGF-1 and growth hormone deficiency
Low IGF-1 can occur when the pituitary does not produce enough growth hormone or when the body cannot generate normal IGF-1 responses. In children, this may be considered during evaluation of poor growth velocity or short stature. In adults, true growth hormone deficiency is usually evaluated in people with a clear risk factor, such as pituitary disease, pituitary surgery, cranial radiation, traumatic brain injury, or multiple pituitary hormone deficiencies.
Importantly, low IGF-1 is not specific. Nutrition, liver function, thyroid status, diabetes control, inflammatory illness, and medications can all influence the result. The Endotext chapter on adult growth hormone stimulation testing explains that adult growth hormone deficiency generally cannot be established in most patients from a single random IGF-1 or growth hormone measurement.
What is an IGF-1 z-score?
A z-score shows how far your IGF-1 result is from the average of the reference population used by that lab. A z-score of 0 is near the average. A z-score of +2 means the result is about two standard deviations above the average, while -2 is about two standard deviations below. Many labs consider values between about -2 and +2 to be within the expected statistical range, but your clinician interprets the z-score together with symptoms, age, puberty status, medical history, and the assay method.
Factors that can affect IGF-1 results
IGF-1 interpretation is sensitive to context. A single result can be misleading if the laboratory method, reference range, health status, or medication history is overlooked.
- Age and puberty: IGF-1 rises during puberty and declines across adulthood.
- Sex and estrogen exposure: Oral estrogen therapy can reduce hepatic IGF-1 production and affect interpretation of growth hormone status.
- Nutrition and body weight: Undernutrition, eating disorders, and significant illness may lower IGF-1.
- Liver disease: Because the liver is the major source of circulating IGF-1, liver disease can reduce levels.
- Diabetes and metabolic control: Poorly controlled diabetes can affect the growth hormone-IGF-1 axis.
- Thyroid disease: Hypothyroidism may contribute to low IGF-1 and growth issues.
- Pregnancy: Pregnancy changes multiple endocrine pathways and requires clinician-specific interpretation.
- Medications and hormones: Prescribed growth hormone, glucocorticoids, estrogen therapy, and non-prescribed growth hormone secretagogues or peptides can affect results.
- Assay differences: Results from different laboratories may not match exactly, even when measuring the same analyte.
- Biotin and assay interference: High-dose biotin can interfere with some immunoassays; always follow lab-specific instructions.
How much does an IGF-1 blood test cost?
Cost depends on whether the test is ordered through a clinician and billed to insurance, purchased directly through a lab service, or bundled with other endocrine testing. Insurance coverage depends on medical necessity, diagnosis codes, deductibles, copays, and network rules. If you are paying cash, compare the effective total cost, not just the advertised test price.
The examples below are consumer-facing self-pay prices observed from public ordering pages and are not rankings. Availability, age rules, state restrictions, lab network access, and fees can change. Confirm the final checkout total before purchasing.
| Ordering route example | Advertised IGF-1 test price | Mandatory fee shown | Effective cost to the patient shown | Collection / result notes |
|---|---|---|---|---|
| JustLabs IGF-1 | $24 | $28 standard lab and physician fees at checkout, described as $18 collection plus $10 physician order | $52 | Quest network listed; page states fasting not required and typical results in 2–3 business days. |
| Walk-In Lab IGF-1 | $75 | $6 per-order physician fee | $81 | Page lists blood specimen, no fasting required, biotin avoidance instruction, and estimated results in 6–8 days. |
| Labcorp OnDemand IGF-1 | $139 | No separate mandatory fee shown on the product page reviewed | $139 | In-person Labcorp collection; page states results 2–4 days from when the sample arrives at the lab and age 18–100. |
When comparing options, check five things: the final total including order and draw fees; whether the lab network has a convenient collection site; whether your state allows that ordering model; whether the report includes the z-score you need; and whether the result will be easy to share with your clinician. For a medically complex concern such as suspected acromegaly or pituitary disease, ordering through your healthcare team may be more useful than buying a stand-alone test because follow-up testing and interpretation are often needed.
What to do after you get results
Use your IGF-1 result as a starting point for a structured conversation, not as a self-diagnosis. The best next step depends on the result pattern and why the test was ordered.
If your IGF-1 is high
- Review the result with the age- and sex-specific range and z-score.
- Confirm whether you were taking biotin, growth hormone, secretagogues, peptides, or other hormones that could affect the test.
- Ask whether the test should be repeated using the same laboratory method.
- If acromegaly is suspected, ask whether growth hormone suppression testing after oral glucose is appropriate.
- If biochemical testing supports acromegaly, pituitary MRI and endocrinology referral are common next steps.
If your IGF-1 is low
- Review nutrition, weight change, liver function, thyroid status, diabetes control, chronic illness, and medications.
- For children, interpretation should be paired with growth charts, growth velocity, puberty stage, bone age, and pediatric endocrinology input when indicated.
- For adults, ask whether your medical history creates a high enough pretest probability for growth hormone stimulation testing.
- Do not start growth hormone without a clinician’s diagnosis and monitoring plan.
If your result is normal but symptoms continue
A normal IGF-1 can be reassuring, but it does not explain every symptom. Fatigue, body composition changes, headaches, joint pain, menstrual changes, libido changes, sleep apnea, and changes in glucose control can have many causes. Your clinician may evaluate thyroid function, prolactin, cortisol, sex hormones, metabolic markers, sleep quality, medication effects, or other conditions depending on your symptoms.
IGF-1 vs. related tests
| Test | What it helps evaluate | How it differs from IGF-1 |
|---|---|---|
| Growth hormone blood test | Direct GH level at the time of draw | Random GH is highly variable because secretion is pulsatile. |
| Oral glucose GH suppression test | Confirmation of suspected acromegaly | Checks whether GH suppresses appropriately after glucose; often used after high IGF-1. |
| Growth hormone stimulation test | Possible growth hormone deficiency | Measures GH response to a stimulus under supervised conditions. |
| IGFBP-3 | Growth hormone axis support, especially in some pediatric evaluations | Measures an IGF-binding protein; may be used with IGF-1 but does not replace clinical interpretation. |
| Pituitary MRI | Structural pituitary causes after biochemical evidence | Imaging is not a substitute for biochemical testing and is usually ordered when lab and clinical findings justify it. |
FAQs about the IGF-1 blood test
Is IGF-1 the same as HGH?
No. HGH, or human growth hormone, is produced by the pituitary gland. IGF-1 is produced mainly by the liver in response to growth hormone. IGF-1 reflects growth hormone activity more steadily than a random HGH measurement.
Do I need to fast before an IGF-1 blood test?
Most IGF-1 tests do not require fasting. However, if your clinician orders IGF-1 with glucose, insulin, lipids, or other fasting tests, you may be asked to fast for the panel. Always follow the instructions on your order.
Can biotin affect IGF-1 results?
It depends on the assay used by the laboratory. Biotin can interfere with some immunoassays, and many labs recommend avoiding high-dose biotin for a defined period before certain hormone tests. Because supplement doses vary widely, ask the ordering clinician or laboratory what to do for your specific test.
What is a normal IGF-1 level?
There is no single normal number for everyone. IGF-1 varies by age, sex, pubertal stage, and lab method. Use the reference interval and z-score on your own report rather than a generic online range.
Does high IGF-1 always mean acromegaly?
No. Persistently high IGF-1 can raise concern for acromegaly, especially when symptoms fit, but the result should be confirmed and interpreted by a clinician. Puberty, pregnancy, lab variation, medications, and hormone use can affect results.
Does low IGF-1 always mean growth hormone deficiency?
No. Low IGF-1 can support the diagnosis in the right setting, but it can also be caused by poor nutrition, liver disease, uncontrolled diabetes, hypothyroidism, chronic illness, and some medications. Dynamic testing may be needed if growth hormone deficiency is strongly suspected.
Can I use IGF-1 to monitor anti-aging or fitness peptides?
IGF-1 may change with substances that affect growth hormone pathways, but using the test to self-manage non-prescribed hormones or peptides is risky. High or low IGF-1 can have medical implications, and hormone manipulation should be discussed with a qualified clinician.
Should children and adults interpret IGF-1 the same way?
No. Children and adolescents require interpretation based on age, sex, puberty stage, growth velocity, and sometimes bone age. Adult interpretation focuses more on pituitary history, symptoms, medication context, and whether dynamic testing is needed.
How often should IGF-1 be repeated?
Repeat timing depends on why it was ordered. Monitoring acromegaly treatment or prescribed growth hormone therapy may require periodic testing. A borderline or unexpected result may be repeated sooner, ideally using the same lab method. Follow the plan from the ordering clinician.
Sources
- MedlinePlus: IGF-1 (Insulin-like Growth Factor 1) Test
- Mayo Clinic Laboratories: IGF-1, LC/MS test catalog
- Endocrine Society Clinical Practice Guideline: Acromegaly
- Endocrine Society Clinical Practice Guideline: Adult Growth Hormone Deficiency
- ARUP Consult: Acromegaly
- ARUP Consult: Growth Hormone Deficiency
- Endotext: Growth Hormone Stimulation Tests in Assessing Adult Growth Hormone Deficiency
- U.S. Food and Drug Administration: Biotin Interference with Lab Tests
Educational note
This article is for general education about IGF-1 testing and result interpretation. It is not a diagnosis or a substitute for care from a licensed healthcare professional. If your result is high, low, or inconsistent with your symptoms, review it with the clinician who ordered the test or an endocrinology specialist.
