An insulin-like growth factor 1 (IGF-1) blood test result cannot be interpreted without your date of birth. At Longevity Benchmark, we track endocrine biomarkers to separate verified reference intervals from speculative longevity claims. Circulating IGF-1 levels by age drop by more than half between adolescence and older adulthood across every major laboratory registry.
The Verdict
IGF-1 Levels by Age Across Human Development
Circulating concentrations of insulin-like growth factor 1 change continuously across the human lifespan in response to pituitary growth hormone secretion. The liver produces IGF-1 following stimulation by pulsatile growth hormone bursts from the pituitary gland. According to published data from ZRT Laboratory, circulating levels remain low in early childhood, rise sharply to peak during the pubertal growth spurt, and decline steadily throughout adult life.
Unbound IGF-1 has a biological half-life of only 10 minutes in human circulation. To stabilize the hormone, specialized binding proteins bind nearly all circulating peptide. A study indexed in PubMed Central notes that a ternary complex composed of IGF-1, IGF-binding protein 3, and an acid-labile subunit extends the circulating half-life to more than 12 hours.
This molecular stability explains why clinicians measure IGF-1 rather than growth hormone itself. Growth hormone pulses intermittently with a half-life of 20 to 25 minutes, making random measurements uninformative. This guide is not for individuals undergoing active clinical evaluation for suspected pituitary tumors or severe hypopituitarism, who require supervised dynamic endocrine testing.
Labcorp Reference Intervals for IGF-1 Levels by Age
Commercial reference intervals establish normal boundaries for specific analytical platforms rather than universal biological constants. The table below lists reference ranges from Labcorp test 010363, which uses the IDS-iSYS immunochemiluminometric assay calibrated to WHO reference standard 02/254. Labcorp derived these intervals from 778,173 males and 710,752 females across the United States using a modified Hoffman method.
Peak female concentrations occur around age 13 with an upper limit of 678 ng/mL, while male concentrations peak at age 16 with an upper limit of 748 ng/mL. After age 20, both upper and lower reference limits drop continuously through every subsequent five-year interval. For individuals older than 90 years, Labcorp explicitly notes that reference intervals are not established.
| Age Group | Male Range (ng/mL) | Female Range (ng/mL) |
|---|---|---|
| Age <1 | 18 to 79 | 14 to 106 |
| Age 5 | 37 to 196 | 46 to 243 |
| Age 12 | 87 to 519 | 110 to 656 |
| Age 13 | 101 to 620 | 150 to 678 |
| Age 15 | 161 to 760 | 156 to 586 |
| Age 16 | 171 to 748 | 140 to 517 |
| Age 18 | 145 to 506 | 117 to 430 |
| Age 20 | 116 to 410 | 108 to 384 |
| Ages 21 to 25 | 109 to 353 | 101 to 347 |
| Ages 26 to 30 | 101 to 307 | 91 to 308 |
| Ages 31 to 35 | 95 to 290 | 84 to 281 |
| Ages 36 to 40 | 90 to 278 | 79 to 259 |
| Ages 41 to 45 | 84 to 270 | 74 to 239 |
| Ages 46 to 50 | 81 to 263 | 70 to 225 |
| Ages 51 to 55 | 74 to 255 | 65 to 216 |
| Ages 56 to 60 | 68 to 247 | 60 to 207 |
| Ages 61 to 65 | 64 to 240 | 57 to 202 |
| Ages 66 to 70 | 59 to 230 | 52 to 196 |
| Ages 71 to 75 | 53 to 222 | 48 to 191 |
| Ages 76 to 80 | 45 to 207 | 42 to 185 |
| Ages 81 to 85 | 40 to 194 | 39 to 177 |
| Ages 86 to 90 | 33 to 176 | 34 to 169 |
| Age >90 | Not established | Not established |
ARUP Intervals and Variation in IGF-1 Levels by Age
Comparing reference intervals across major diagnostic facilities demonstrates that laboratory thresholds are platform-dependent. The data below shows reference values published for the ARUP quantitative chemiluminescent immunoassay across selected adult milestones. ARUP establishes single-year reference bands rather than five-year brackets and terminates its reference ranges at age 85.
| Age Milestone | ARUP Male Range (ng/mL) | ARUP Female Range (ng/mL) |
|---|---|---|
| Age 0 | 11 to 100 | 8 to 131 |
| Age 14 | 83 to 519 | 115 to 591 |
| Age 18 | 137 to 461 | 117 to 436 |
| Age 25 | 99 to 283 | 100 to 311 |
| Age 30 | 83 to 246 | 89 to 290 |
| Age 40 | 82 to 237 | 76 to 271 |
| Age 50 | 67 to 225 | 57 to 236 |
| Age 60 | 53 to 206 | 43 to 241 |
| Age 70 | 27 to 246 | 26 to 226 |
| Age 80 | 18 to 184 | 18 to 200 |
| Age 85 | 15 to 177 | 17 to 167 |
Technical Causes of Laboratory Discrepancies
Analytical differences between laboratories stem from antibody specificity, standard drift, and demographic variations. A review published by Clemmons and Bidlingmaier in the European Journal of Endocrinology examined six commercial immunoassays and found substantial bias in absolute reported concentrations. Furthermore, evaluations of 32 lots of pure standard over five years on the Siemens Immulite 2000 platform revealed substantial drift that altered patient results regardless of technician handling.
Reference cohorts also shift across geographic boundaries even when using the identical analytical instrument. Research by Bidlingmaier and colleagues in the Journal of the Endocrine Society compared routine clinical samples between the United States and Europe on the IDS assay. In adult populations, upper limits in the United States were 45 ng/mL higher in men and 29.7 ng/mL higher in women compared to European cohorts.
This geographical divergence alters clinical interpretations directly. An IGF-1 level of 260 ng/mL in a 50-year-old man exceeds 1.2 times the upper normal limit under European standards, yet registers as normal under United States intervals. Our guide to normal vs optimal reference ranges explains how population selection alters laboratory cutoffs.
Standard Deviation Scores and Practical Measurement Limits
A standard deviation score expresses how far an individual result deviates from the age- and sex-adjusted population mean. Also known as a z-score, this metric requires both patient age and sex at the time of requisition. Labcorp test 010540 reports raw mass in ng/mL alongside this standardized score, where values between -2.0 and +2.0 standard deviations represent the central 95 percent of the reference cohort.
Clinicians use z-scores to monitor growth hormone therapy and assess pituitary pathology without recalculating raw thresholds across birthdays. A 2023 international consensus in Pituitary noted that while thorough age stratification remains necessary, sex stratification beyond puberty is less critical when normative cohorts are large. However, converting to a z-score does not resolve inter-laboratory discrepancies.
Clemmons and Bidlingmaier demonstrated that while standard deviation scores align between some assay pairs, other commercial platforms show wide discrepancies that persist after mathematical transformation. A z-score calculated by one laboratory cannot be compared against a score from another facility. The authors recommend relying on a single centralized laboratory for longitudinal tracking and repeating any measurement that contradicts the clinical presentation.
Clinical Indications of a High Result
Markedly high circulating IGF-1 indicates autonomous growth hormone hypersecretion or physiological adaptations such as pregnancy. The National Institute of Diabetes and Digestive and Kidney Diseases notes that acromegaly affects between 3 and 14 individuals per 100,000, stemming from a benign pituitary adenoma in over 90 percent of cases. During normal pregnancy, placental production of growth hormone variants also increases maternal serum IGF-1 concentrations.
Diagnostic criteria require rigorous biochemical confirmation before establishing a diagnosis of growth hormone excess. An international consensus published in Pituitary states that an IGF-1 concentration exceeding 1.3 times the age-specific upper limit of normal in a symptomatic patient confirms acromegaly. The Endocrine Society acromegaly guideline emphasizes that an isolated high IGF-1 level requires confirmation by demonstrating failure of growth hormone to suppress below 1 mcg/L during an oral glucose load.
Elevated levels correlate with headaches, joint pain, excessive sweating, and soft tissue enlargement, though symptoms vary widely across individuals. In oncology, data published by ZRT Laboratory indicates that the mitogenic and anti-apoptotic properties of IGF-1 link the hormone to several malignancies, including colorectal, lung, prostate, and premenopausal breast cancers. Meta-analyses show that these cancer associations remain modest and variable across study cohorts, frequently confounded by nutritional factors and body mass index.
Clinical Indications of a Suppressed Result
Suppressed circulating IGF-1 indicates hypopituitarism, systemic catabolic disease, or acute caloric restriction. According to the Endocrine Society adult growth hormone deficiency guideline, a low IGF-1 in the absence of catabolic conditions provides strong evidence for severe deficiency. However, a normal IGF-1 level does not exclude growth hormone deficiency, making provocative stimulation testing mandatory when clinical suspicion exists.
Nutritional intake directly modulates hepatic synthesis independent of pituitary function. Labcorp documentation notes that malnutrition depresses IGF-1 levels despite normal or elevated concentrations of circulating growth hormone. In a study published by Bang and colleagues in the Journal of Clinical Endocrinology and Metabolism, four days of complete fasting reduced serum IGF-1 by 37 percent in healthy non-obese individuals.
Because synthesis responds rapidly to nutrient availability, clinicians use IGF-1 as a sensitive indicator of nutritional recovery in eating disorders. Conversely, poorly controlled type 2 diabetes, chronic liver cirrhosis, and oral estrogen therapy suppress circulating concentrations. Low levels correlate clinically with fatigue, decreased muscle mass, increased visceral adiposity, and reduced bone density, requiring careful evaluation of underlying metabolic health.
The Unresolved Relationship With Longevity and Mortality
The hypothesis that suppressing IGF-1 extends human life draws support from animal genetics but faces contradictory epidemiological evidence. A foundational study by Holzenberger and colleagues in Nature demonstrated that heterozygous IGF-1 receptor knockout mice lived 26 percent longer than wild-type littermates. Female knockout mice lived 33 percent longer than wild-type females (P < 0.001), whereas the 16 percent increase in male mice was not statistically significant. Even in mice the result depends on sex.
Human cohort studies display divergent outcomes across different sexes and age brackets. Research by Milman and colleagues in Aging Cell evaluated 184 nonagenarians and found that females with IGF-1 below 96 ng/mL had longer survival, whereas males showed no survival difference. Conversely, a cross-sectional study by Doi and colleagues in the Journal of Nutrition, Health and Aging linked the lowest IGF-1 quartile to 1.54 times higher adjusted odds of clinical frailty.
General population cohorts consistently identify a U-shaped association between circulating IGF-1 and all-cause mortality. A meta-analysis by Burgers and colleagues in the Journal of Clinical Endocrinology and Metabolism analyzing 14,906 participants found that both low concentrations (hazard ratio 1.27) and high concentrations (hazard ratio 1.18) associated with increased mortality. In 380,997 participants from the UK Biobank, Xie and colleagues reported in the European Journal of Endocrinology that the lowest decile had 39 percent higher all-cause mortality while the highest decile had 17 percent higher mortality.
A 2022 meta-analysis by Rahmani and colleagues in Aging Cell noted that values between 120 and 160 ng/mL correlated with lowest mortality, but this pooled window cannot serve as a clinical target because it ignores age adjustments and assay differences. What would change our assessment is a randomized trial demonstrating that deliberately lowering IGF-1 in healthy adults extends healthspan without promoting sarcopenia. Readers exploring aging metrics can review our analysis of what biological age measures.
Dietary Protein and the CALERIE Study Findings
Caloric restriction alone does not reduce circulating IGF-1 concentrations in humans when protein consumption remains elevated. In the CALERIE trial published by Fontana and colleagues in Aging Cell, healthy non-obese adults underwent two years of 25 percent caloric restriction. While the calorie restriction group experienced a 15.1 ng/mL within-group reduction from their 175.5 ng/mL baseline, their levels did not differ statistically from ad libitum controls after 24 months.
The trial authors explained that unlike laboratory rodents, human participants maintained dietary protein intake at approximately twice the recommended daily allowance. Prior metabolic research cited by the authors indicated that reducing dietary protein from 1.6 to 0.95 grams per kilogram of body weight per day was required to depress circulating IGF-1. Readers seeking structured dietary strategies can explore our review of an evidence-based fasting protocol.
Modulating growth factors through lifestyle or secretagogues requires balancing anabolic benefits against theoretical risks. Individuals evaluating therapies for body composition can read our review of sermorelin therapy. Review your laboratory report alongside an endocrinologist to evaluate your IGF-1 levels by age in the context of your overall metabolic health.
Frequently Asked Questions
What is a normal IGF-1 level for my age?
No single universal normal range exists for insulin-like growth factor 1. Because concentrations decline continuously throughout adulthood, results must be compared against age-matched reference intervals specific to the testing laboratory. For example, in the Labcorp IDS-iSYS assay, a 30-year-old male has a published reference interval of 101 to 307 ng/mL, whereas a 70-year-old male has an interval of 59 to 230 ng/mL. In the ARUP chemiluminescent assay, a 70-year-old male reference range is 27 to 246 ng/mL. Because testing platforms introduce systematic bias, always evaluate your result against the age-stratified reference table printed directly on your laboratory report.
What does the Z score on an IGF-1 result mean?
A Z-score, also termed a standard deviation score, indicates how many standard deviations your IGF-1 concentration sits above or below the mean for individuals of your exact age and sex. A score between -2.0 and +2.0 standard deviations corresponds to a value inside the laboratory reference interval, capturing the middle 95 percent of the reference cohort. A positive score denotes a concentration above average, while a negative score indicates a level below average. However, clinical studies show that Z-scores from different commercial laboratories cannot be compared directly due to underlying platform differences.
What does a high IGF-1 level mean?
A high IGF-1 level indicates increased exposure to growth hormone or specific physiological adaptations like pregnancy. Pathological elevations most frequently stem from a benign pituitary adenoma causing acromegaly in adults or gigantism in children. Clinical consensus guidelines establish that an IGF-1 concentration exceeding 1.3 times the age-specific upper limit of normal in an individual with characteristic signs confirms acromegaly, though endocrinologists confirm the condition using an oral glucose tolerance test. Moderately high values can also occur transiently during rapid nutritional recovery, hyperthyroidism, or pubertal growth surges.
What does a low IGF-1 level mean?
A low IGF-1 level suggests reduced growth hormone output, severe malnutrition, or systemic catabolic illness. In adults, low levels can indicate hypopituitarism or adult growth hormone deficiency, though clinical guidelines require confirmatory stimulation testing because a normal IGF-1 does not rule out growth hormone deficiency. Furthermore, circulating IGF-1 drops rapidly during caloric deprivation, extended fasting, poorly controlled type 2 diabetes, or advanced liver disease. Because the liver synthesizes IGF-1 in response to growth hormone, hepatic dysfunction reduces circulating levels even when pituitary growth hormone output is normal.
Do IGF-1 levels differ between men and women?
IGF-1 concentrations vary by sex, primarily during development and late adulthood. During adolescence, female levels peak earlier than male levels, corresponding with earlier pubertal growth spurts. In the Labcorp reference dataset, the female median peak occurs around age 13 (150 to 678 ng/mL), whereas the male peak occurs around age 16 (171 to 748 ng/mL). Throughout mid-adulthood, male and female reference intervals overlap substantially, but oral estrogen therapy in women substantially suppresses circulating IGF-1 by impeding hepatic synthesis, requiring sex-specific evaluation.
Is lower IGF-1 better for longevity?
Scientific evidence does not support the claim that lower IGF-1 levels extend human lifespan. While reduced growth factor signaling extends lifespan in certain mouse models, human epidemiological data reveals a complex U-shaped relationship. In large cohorts like the UK Biobank, individuals in both the lowest and highest deciles of circulating IGF-1 exhibit higher all-cause and cardiovascular mortality. Furthermore, low IGF-1 in older adults is strongly associated with muscle wasting and frailty. In an Ecuadorian cohort with congenital growth hormone receptor deficiency and lifelong IGF-1 levels below 20 ng/mL, individuals had no cases of diabetes and one nonlethal malignancy, against a prevalence of 5 percent and 17 percent respectively in controls, but did not live longer than unaffected relatives. No intervention trial has proven that lowering IGF-1 improves human healthspan.
Can you compare IGF-1 results from two different labs?
You cannot reliably compare raw IGF-1 numbers or Z-scores from two different laboratories. Commercial assays use distinct antibodies, calibration reagents, and normative population cohorts, producing substantial systematic bias. A 2024 European Journal of Endocrinology review evaluated six commercial immunoassays and documented extensive discrepancies in absolute concentrations, finding that converting raw values to standard deviation scores failed to resolve inter-assay variation. For accurate longitudinal monitoring, clinicians advise having all repeat tests performed by the same laboratory facility using the identical analytical platform.
What affects IGF-1 levels?
Multiple physiological, dietary, and medical factors influence circulating IGF-1 concentrations. Beyond age and sex, nutritional status is the most potent modulator. Multi-day fasting can reduce serum IGF-1 by over 30 percent, and chronic protein restriction below 1.0 gram per kilogram of body weight substantially lowers circulating levels. Conversely, conditions such as uncontrolled diabetes, hypothyroidism, cirrhosis, and oral estrogen therapy suppress hepatic IGF-1 synthesis. Systemic inflammation and acute catabolic illness also depress levels, while pregnancy and excessive growth hormone secretion drive values upward.