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IGF-1 Z-Score (SDS)

A score that shows how far your IGF-1 result is from the average for people of your age and sex, in standard deviations. Labs usually print it next to IGF-1.

AI-verified against cited sources. Awaiting expert reviewAlso called IGF-1 SDS, IGF-I SDSLOINC 73561-3

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What it is

An IGF-1 Z-score, also called an SD score, tells you how far your IGF-1 result is from the average for people of your age and sex. A score of 0 means average. A score of +1 or -1 means one standard deviation above or below average. A result inside the lab's IGF-1 reference range has a score between -2.0 and +2.0. Your lab works the score out from its own reference data. It is printed next to your IGF-1 result and can't be compared directly with a score from a different lab or method.

Why it matters

IGF-1 changes a lot with age and differs between men and women, so the raw number is hard to judge. Turning it into a score shows at a glance where you sit for your age and sex, including in children and teenagers. Clinicians use IGF-1 to look at growth hormone activity. A low score is one reason to look further for growth hormone deficiency, and a high score can prompt more testing for too much growth hormone (acromegaly). IGF-1 also falls with poor nutrition, liver disease and poorly controlled diabetes, so a low score doesn't always point to a growth hormone problem.

If it’s low

A score below -2 means your IGF-1 is lower than that of most people your age and sex, as reported by your lab. This is often linked to things that affect how the liver responds to growth hormone, such as poor nutrition, liver disease, poorly controlled diabetes, kidney failure or oral estrogen. Less often it reflects low growth hormone from the pituitary gland. A low score alone does not show growth hormone deficiency, and clinicians usually look at other pituitary hormones and sometimes a stimulation test.

Common causes

  • Not eating enough calories or protein, or long-term illness
  • Poorly controlled diabetes
  • Liver disease or kidney failure
  • Oral estrogen therapy, which blunts the liver's response to growth hormone
  • A high-dose biotin supplement interfering with some assays
  • Low growth hormone from the pituitary gland (uncommon)

What can help

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

If it’s high

A score above +2 means your IGF-1 is higher than that of most people your age and sex, as reported by your lab. Pregnancy and growth hormone treatment are common reasons. In children and teens, the stage of puberty matters, which is why some labs give scores by pubertal stage. Less often, a high score is linked to too much growth hormone from a pituitary tumor (acromegaly or gigantism). A clinician can look at your symptoms, repeat the test and add others, such as a glucose suppression test, before drawing any conclusion.

Common causes

  • Pregnancy
  • Growth hormone treatment
  • Puberty in children and teens (the score may depend on pubertal stage)
  • Differences between labs, assays or the age and sex used for the score
  • Acromegaly or gigantism, caused by a growth hormone-making pituitary tumor (uncommon)

What can help

  • Ask your clinician whether the score was worked out for your correct age and sex, and your stage of puberty if you are a teen
  • Ask whether 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.

For adults: -2–2 SD. Source: Quest Diagnostics, ARUP Laboratories, Journal of Clinical Medicine, Mayo Clinic Laboratories.

What can affect your result

  • Age and sex: the score compares you with people of the same age and sex
  • Pubertal stage in children and teens
  • Nutrition, liver disease, kidney disease and diabetes control
  • Oral estrogen, pregnancy and growth hormone treatment
  • The lab's assay and reference data: scores aren't portable between labs
  • High-dose biotin can interfere with some assays
  • Your age and sex have to be on the order. Labcorp and ARUP can't calculate a Z-score without them.
  • Z-scores are calculated by each lab from its own IGF-1 assay and reference data, so a score from one lab or method can't be compared with another.
  • High-dose biotin (vitamin B7) can interfere with some IGF-1 assays. Labcorp advises stopping biotin at least 72 hours before the draw unless your clinician says otherwise.
  • Anything that changes IGF-1 changes the score: nutrition, liver disease, poorly controlled diabetes, kidney failure, oral estrogen, pregnancy and growth hormone treatment.

Any time of day. IGF-1 stays fairly steady through the day. IGF-1 changes slowly, over days to weeks, with growth hormone levels and nutrition.

When to talk to a clinician

There is no emergency threshold for an IGF-1 Z-score. Talk with the clinician who ordered it if your score is below -2 or above +2, especially if you notice growing hands or feet, changing facial features or joint pain, or if a child is growing slowly. A score outside the range is a reason for a conversation, not an emergency.

Questions you could ask

  • Should I use the same lab each time so scores can be compared?
  • What range or score should we aim for, given my situation?
  • Was this score worked out for my correct age and sex?
  • Could pregnancy or treatment explain it?
  • Would a growth hormone suppression test or other pituitary tests add useful information?
  • Could nutrition, liver or kidney health, diabetes control or oral estrogen explain this score?

Questions people ask

What does a score of -1.5 or +1.5 mean?

It means your IGF-1 is one and a half standard deviations below or above the average for people of your age and sex. Both are inside the usual -2 to +2 span. A score is a way to compare you with others of your age and sex, not a measure of health on its own.

Can I compare Z-scores from different labs?

Not directly. Each lab calculates the score from its own assay and reference data, and IGF-1 assays can differ a lot. Compare scores from the same lab and method, and bring both your IGF-1 value and your score when you talk with your clinician.

Is a score close to 0 the best result?

Not necessarily. Most people are within -2 to +2. For people having growth hormone treatment, Mayo describes aiming for the reference range, ideally the middle to upper third, while for treated acromegaly it describes the lower third. Your clinician will talk through the aim that fits your situation.

Show the science and sources

For clinicians and researchers

An IGF-1 Z-score (SD score) is the number of standard deviations a result is above or below the age- and sex-adjusted population mean (ARUP): Z = (measured IGF-1 - mean for age and sex) / SD for age and sex. The reporting lab calculates it from its own IGF-1 assay and reference data, and some labs use transformed data for the asymmetric distributions seen across puberty (Labcorp). Results inside the lab's IGF-1 reference interval have a score between -2.0 and +2.0 (ARUP, Quest). Labcorp's IDS-iSYS reference intervals come from a US clinical-routine cohort of 778,173 males and 710,752 females aged 0-90, adjusted for age and sex with a modified Hoffmann approach and calibrated to WHO standard 02/254. Labcorp warns of considerable differences between the available IGF-1 assays, so scores from different assays aren't interchangeable. ARUP has not established intervals above age 85. Interpreting scores for GH deficiency: as summarized in a 2024 review, adults with three or more pituitary hormone deficits and IGF-I below the reference range have a probability above 97% of also having GH deficiency, while with fewer than two deficits a low IGF-I (below -2 SDS) alone is not sufficient; random GH and IGF-I alone are not reliable for the diagnosis, and most patients need stimulation testing. IGF-1 can fall with protein or caloric malnutrition, poorly controlled diabetes, chronic disease, renal failure and liver cirrhosis, and oral estrogen blunts hepatic sensitivity to GH. Mayo's guidance for monitoring GH replacement is IGF-1 within the reference range, ideally in the middle to upper third, and for treated acromegaly ideally in the lower third. Clinicians interpret scores together with the assay-specific IGF-1 reference interval.

LOINC 73561-3 (primary). Specimen: calculated.

Sources

  1. IGF-1, LC/MS (test code 16293), Quest Diagnostics
  2. Insulin-Like Growth Factor 1 (IGF-1) with Calculated Z-Score (ARUP test 2007698), ARUP Laboratories
  3. Insulin-like Growth Factor 1 (IGF-1) With Z Score (test 010540), Labcorp
  4. Endocrinology Expected Values (IGF-I, Pediatric with Z Score, test 503660), Labcorp (Endocrine Sciences)
  5. A 2024 Update on Growth Hormone Deficiency Syndrome in Adults: From Guidelines to Real Life, Journal of Clinical Medicine (2024)
  6. IGFB3: Insulin-Like Growth Factor-Binding Protein 3, Serum, Mayo Clinic Laboratories

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

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