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IGF-1 (Insulin-like Growth Factor 1)

A protein your liver makes in response to growth hormone. It's a steady signal of growth hormone activity, and usual levels vary a lot with age and sex.

AI-verified against cited sources. Awaiting expert reviewAlso called IGF-1, IGF-I, IGF1LOINC 2484-4

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The usual range for IGF-1 depends on sex. Choose female or male above to see where you stand.

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What it is

IGF-1 is a small protein made mostly in the liver when growth hormone from the pituitary gland tells it to. It helps children grow, and in adults it plays a role in building and maintaining body tissues. Growth hormone is released in short bursts, but IGF-1 stays steady through the day, so one blood test gives a good picture of recent growth hormone activity. Levels rise through childhood, peak during the teen years, then slowly decline with age.

Why it matters

Clinicians use IGF-1 to look at whether the body has too much or too little growth hormone, and to follow treatment for those conditions. It also drops with poor nutrition, liver disease and poorly controlled diabetes, so it can also reflect nutrition and general health. Because usual values change so much with age and sex, and differ between lab methods, a result should always be read against the range on your own lab report.

If it’s low

A low result for your age can be linked to things that affect how the liver responds to growth hormone, such as poor nutrition, liver disease, poorly controlled diabetes or oral estrogen. Less often it reflects low growth hormone from the pituitary gland. A low IGF-1 doesn't prove low growth hormone, and a result in the usual range doesn't rule it out, so clinicians also look at your symptoms and other tests.

Common causes

  • Older age, since levels decline naturally
  • Malnutrition or very low food intake, including anorexia
  • Liver disease
  • Poorly controlled diabetes
  • Oral estrogen therapy, which blunts the liver's response to growth hormone
  • High-dose biotin supplements, which can make some IGF-1 tests read low
  • Low growth hormone from the pituitary gland (uncommon)

What can help

  • Ask your clinician whether nutrition, liver health, diabetes control or oral estrogen could be affecting this number
  • Ask whether growth hormone or other pituitary hormone testing is worth discussing
  • Tell your clinician about any biotin supplement before a repeat test

If it’s high

A high result for your age can mean the body is making more growth hormone than usual, which is uncommon. It can also reflect pregnancy or growth hormone treatment. Usual values change so much across a lifetime that your lab's range for your age and sex matters here. A clinician can look at your symptoms and decide whether more testing makes sense.

Common causes

  • Pregnancy, when levels normally rise
  • Puberty and teen growth spurts, when levels are naturally highest (check the range for your age)
  • Growth hormone treatment that gives the body more than it needs
  • Acromegaly or gigantism, caused by too much growth hormone from a pituitary tumor (uncommon)

What can help

  • Ask your clinician whether your result fits the range for your age and sex on your lab's report
  • Ask whether more testing, such as a growth hormone suppression test, would add useful information
  • Repeat with the same lab and method if your clinician wants to follow it over time

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 36 ranges
  • Men, under 118–79 ng/mL

    Source: Labcorp

  • Women, under 114–106 ng/mL

    Source: Labcorp

  • Men, 120–108 ng/mL

    Source: Labcorp

  • Women, 123–136 ng/mL

    Source: Labcorp

  • Men, 224–135 ng/mL

    Source: Labcorp

  • Women, 230–163 ng/mL

    Source: Labcorp

  • Men, 328–148 ng/mL

    Source: Labcorp

  • Women, 334–192 ng/mL

    Source: Labcorp

  • Men, 432–165 ng/mL

    Source: Labcorp

  • Women, 438–217 ng/mL

    Source: Labcorp

  • Men, 537–196 ng/mL

    Source: Labcorp

  • Women, 546–243 ng/mL

    Source: Labcorp

  • Men, 643–229 ng/mL

    Source: Labcorp

  • Women, 656–268 ng/mL

    Source: Labcorp

  • Men, 750–243 ng/mL

    Source: Labcorp

  • Women, 764–288 ng/mL

    Source: Labcorp

  • Men, 859–275 ng/mL

    Source: Labcorp

  • Women, 874–337 ng/mL

    Source: Labcorp

  • Men, 967–315 ng/mL

    Source: Labcorp

  • Women, 981–405 ng/mL

    Source: Labcorp

  • Men, 1075–366 ng/mL

    Source: Labcorp

  • Women, 1085–526 ng/mL

    Source: Labcorp

  • Men, 1182–423 ng/mL

    Source: Labcorp

  • Women, 1191–610 ng/mL

    Source: Labcorp

  • Men, 1287–519 ng/mL

    Source: Labcorp

  • Women, 12110–656 ng/mL

    Source: Labcorp

  • Men, 13101–620 ng/mL

    Source: Labcorp

  • Women, 13150–678 ng/mL

    Source: Labcorp

  • Men, 14123–701 ng/mL

    Source: Labcorp

  • Women, 14174–656 ng/mL

    Source: Labcorp

  • Men, 15161–760 ng/mL

    Source: Labcorp

  • Women, 15156–586 ng/mL

    Source: Labcorp

  • Men, 16171–748 ng/mL

    Source: Labcorp

  • Women, 16140–517 ng/mL

    Source: Labcorp

  • Men, 17161–635 ng/mL

    Source: Labcorp

  • Women, 17130–471 ng/mL

    Source: Labcorp

See IGF-1 by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: levels peak during the teen years, then decline through adult life
  • Sex: many labs give separate ranges for men and women
  • Nutrition: low food intake lowers IGF-1, and it recovers when nutrition is restored
  • Liver disease, poorly controlled diabetes and oral estrogen lower it
  • Pregnancy raises it
  • Assay method: mass spectrometry and immunoassays differ, so compare results from the same method
  • High-dose biotin can make some tests read falsely low
  • High-dose biotin (vitamin B7) can make some IGF-1 tests read falsely low (Mayo); Labcorp advises stopping biotin at least 72 hours before the draw unless your clinician says otherwise.
  • Assay method: immunoassays and LC-MS/MS give different values, and results from different platforms shouldn't be used interchangeably.
  • Low food intake, liver disease, poorly controlled diabetes, kidney failure and other chronic illness lower IGF-1, and oral estrogen blunts the liver's response to growth hormone (Aversa 2024 review).
  • Pregnancy raises IGF-1, and formal reference intervals for pregnancy have not been established (Mayo).
  • Rarely, heterophile antibodies (usually falsely high) or a hook effect at extremely high levels (falsely low) can distort an immunoassay.
  • Rare IGF-1 protein variants are detected only by some mass-spectrometry methods (Quest).

Any time of day. IGF-1 shows only minor changes through the day (Mayo). Days to weeks. IGF-1 is stable through the day, and the protein-bound form clears with a half-life of about 12 hours (Mayo). Nutrition changes can move it, and it recovers when nutrition is restored.

When to talk to a clinician

There is no emergency threshold for IGF-1. Talk with a clinician if your result is outside your lab's range for your age and sex, especially if you notice growing hand or foot size, changing facial features, or slow growth in a child. A result outside the range is a reason for a conversation, not an emergency.

Questions you could ask

  • Should I use the same lab for repeat IGF-1 tests?
  • How should I read my result next to my age and sex?
  • Could pregnancy, a supplement or a treatment I take explain this result?
  • Would more testing, such as a growth hormone test, add useful information?
  • Does my result fit the age and sex range from my own lab?
  • Could my nutrition, liver health, diabetes control or oral estrogen be affecting this number?

Questions people ask

Why does my IGF-1 range depend on my age and sex?

IGF-1 rises through childhood, peaks during the teen years, then falls slowly through adult life. A value that is typical at 65 would be low for a 20-year-old. Many labs also give separate ranges for men and women, which is why your age and sex are needed to read the result.

Why do two labs give me different IGF-1 numbers?

Labs use different methods. Immunoassays and mass spectrometry (LC-MS/MS) don't agree exactly, and mass spectrometry often reports lower values. Each lab builds its ranges for its own method. For tracking over time, use the same lab and method.

Does a result in the usual range mean my growth hormone is fine?

Not always. IGF-1 can be in the usual range in some people who are short on growth hormone, so clinicians may add other tests when there is a specific question. A result below the range doesn't prove low growth hormone either, because nutrition, liver disease, diabetes and oral estrogen can lower it.

Can biotin supplements change my IGF-1 result?

Yes. Some IGF-1 tests can read falsely low if you take high-dose biotin (vitamin B7), found in some hair-and-nail supplements. Labcorp asks that biotin be stopped at least 72 hours before the draw. Check with your clinician first.

How do I convert ng/mL to nmol/L?

Multiply ng/mL by 0.131, so 200 ng/mL is about 26 nmol/L. To go the other way, multiply nmol/L by 7.65.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 0.1308 nmol/L

Open the IGF-1 unit converter

Is a change real?

IGF-1 naturally varies about 14.6% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 45% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).

For clinicians and researchers

IGF-1 is a 70-amino-acid single-chain protein of about 7.6 kDa. The liver is the main source, under growth hormone (GH) control. Most circulating IGF-1 is bound to IGF-binding proteins, chiefly IGFBP-3. Free IGF-1 clears with a half-life of about 10 minutes and IGFBP-3 in 30 to 90 minutes, but the bound complex clears with a half-life of about 12 hours (Mayo), so IGF-1 shows only minor fluctuation through the day and is a stable, integrated read-out of GH action. Immunoassays must dissociate IGF-1 from its binding proteins; incomplete dissociation can read falsely low (Quest). Labcorp's IDS-iSYS immunoassay is calibrated to WHO reference preparation 02/254, with intervals derived from a US cohort of about 1.5 million people adjusted for age and sex. LC-MS/MS (Quest, Mayo FIGF1) tends to report lower values than electrochemiluminescence immunoassays (Quest cites slopes of 0.63 to 0.84) and can detect rare IGF-1 variants (under 0.5% of patients). Platforms aren't interchangeable, so use one assay for serial monitoring. Results are often also reported as a Z-score (SDS), where -2.0 to +2.0 corresponds to the reference interval (ARUP, Mayo, Quest). A normal IGF-1 does not exclude GH deficiency (Mayo, Quest; Aversa 2024 review of guidelines), and the Endocrine Society's 2011 adult GH deficiency guideline says confirmation by stimulation testing is usually required unless there is a proven genetic or structural cause. IGF-1 is lowered by protein or calorie malnutrition, poorly controlled diabetes, chronic illness, renal failure and liver cirrhosis, and oral (not transdermal) estrogen antagonizes hepatic GH action through first-pass effects (Aversa 2024). In acromegaly, age-normalized IGF-1 signals control (Quest), and in GH replacement Mayo suggests aiming within the reference range, ideally the middle-to-upper third. Biotin can falsely lower results on sandwich immunoassays (Mayo).

LOINC 2484-4 (primary), 29775-4. Specimen: serum.

Sources

  1. Insulin-like Growth Factor 1 (IGF-1) (test 010363), Labcorp
  2. FIGF1: IGF-1, LC/MS, Mayo Clinic Laboratories
  3. IGF1S: Insulin-Like Growth Factor 1, Serum, Mayo Clinic Laboratories
  4. Insulin-Like Growth Factor 1 (IGF-1) with Calculated Z-Score (ARUP test 2007698), ARUP Laboratories
  5. IGF-1, LC/MS test guide (test code 16293), Quest Diagnostics
  6. Evaluation and Treatment of Adult Growth Hormone Deficiency: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2011)
  7. A 2024 Update on Growth Hormone Deficiency Syndrome in Adults: From Guidelines to Real Life, Journal of Clinical Medicine (2024)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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