IGF-1

Insulin-Like Growth Factor 1

Hormones

What is Insulin-Like Growth Factor 1?

Insulin-like growth factor 1 (IGF-1), also known as somatomedin C, is a peptide hormone with structural similarity to insulin that mediates many of growth hormone's (GH) effects throughout the body. IGF-1 is produced primarily by the liver in response to GH stimulation, though nearly every tissue produces IGF-1 locally for autocrine and paracrine signaling. In the bloodstream, IGF-1 circulates predominantly bound to IGF-binding protein 3 (IGFBP-3) and an acid-labile subunit (ALS), forming a ternary complex that extends its half-life to 12–15 hours and provides stable circulating levels.

Unlike GH, which is secreted in pulses with wide fluctuations throughout the day, IGF-1 levels are relatively stable, making it an excellent and practical marker of integrated GH activity. IGF-1 promotes growth by stimulating cell proliferation and differentiation in bone, cartilage, muscle, and other tissues. It also has insulin-like metabolic effects including glucose uptake and protein synthesis. IGF-1 levels are influenced by age (peaking during puberty, declining with age), nutritional status, liver function, and GH secretion.

Why It Matters

IGF-1 is the primary screening test for both GH excess (acromegaly) and GH deficiency because it reflects integrated GH secretion without the confounding pulsatile variation of GH itself. An elevated IGF-1 in an adult is the first biochemical clue to acromegaly and triggers confirmatory testing with an oral glucose tolerance test. A low IGF-1 in a child with poor growth suggests GH deficiency and prompts GH stimulation testing. IGF-1 is also used to monitor treatment response in acromegaly (goal: normalize IGF-1) and to guide GH replacement dosing in GH-deficient patients. Beyond endocrinology, IGF-1 is relevant to cancer biology, as the IGF-1 pathway promotes cell proliferation and inhibits apoptosis.

Normal Reference Ranges

GroupRangeUnit
Children (6–8 years)88–474ng/mL
Adolescents (14–16 years)226–903ng/mL
Adults (20–30 years)117–329ng/mL
Adults (40–50 years)94–267ng/mL
Adults (60–70 years)53–206ng/mL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High IGF-1 Levels Mean

Common Causes

  • Acromegaly (GH-producing pituitary adenoma)
  • Gigantism (GH excess before growth plate closure)
  • Puberty (physiologically elevated)
  • High protein diet
  • Exogenous GH administration
  • Pregnancy (modest increase)

Possible Symptoms

  • Acral enlargement (hands, feet, jaw)
  • Coarsened facial features
  • Excessive sweating
  • Joint pain and osteoarthritis
  • Carpal tunnel syndrome
  • Sleep apnea
  • Hypertension and cardiac enlargement
  • Insulin resistance and diabetes

What to do: Elevated age-adjusted IGF-1 is the screening test for acromegaly. Confirmatory testing is the oral glucose tolerance test (OGTT) with GH measurement—failure of GH to suppress below 0.3 ng/mL after glucose load confirms autonomous GH secretion. Pituitary MRI identifies the adenoma. First-line treatment is transsphenoidal surgery. IGF-1 is the primary marker for monitoring treatment success—the goal is normalization of IGF-1 for age and sex. If IGF-1 remains elevated post-surgery, medical therapy with somatostatin analogs (octreotide LAR, lanreotide), pegvisomant (GH receptor antagonist), or combination therapy is used.

What Low IGF-1 Levels Mean

Common Causes

  • GH deficiency (congenital or acquired)
  • GH insensitivity (Laron syndrome—GH receptor defects)
  • Malnutrition and caloric restriction
  • Liver disease (cirrhosis—impaired IGF-1 production)
  • Uncontrolled type 1 diabetes
  • Hypothyroidism (reduces GH action)
  • Normal aging
  • Chronic illness and systemic inflammation

Possible Symptoms

  • Growth failure and short stature in children
  • Delayed skeletal maturation
  • Increased body fat and decreased lean mass in adults
  • Reduced bone density
  • Fatigue and poor exercise tolerance
  • Elevated cholesterol
  • Impaired quality of life

What to do: Low IGF-1 in a child with poor growth warrants GH stimulation testing (insulin tolerance test or glucagon stimulation test) to confirm GH deficiency. Additional evaluation includes bone age X-ray, thyroid function, and pituitary MRI. If GH deficiency is confirmed, GH replacement therapy promotes linear growth—early initiation optimizes adult height. In adults with pituitary disease, low IGF-1 supports the diagnosis of adult GH deficiency, confirmed by stimulation testing. Adult GH replacement improves body composition, bone density, lipids, and quality of life. Nutritional causes (malnutrition, anorexia) are treated by restoring adequate caloric and protein intake.

When Is IGF-1 Testing Recommended?

  • When screening for acromegaly based on clinical features
  • When evaluating growth failure or short stature in children
  • When monitoring treatment response in acromegaly
  • When guiding GH replacement dose in GH-deficient patients

Frequently Asked Questions

GH is secreted in pulses, with levels ranging from undetectable to peaks of 20+ ng/mL throughout the day. A single random GH measurement is therefore unreliable—a normal person between pulses and a GH-deficient person may both have undetectable GH. IGF-1, by contrast, reflects the integrated effect of GH secretion over time and maintains relatively stable levels throughout the day. This makes IGF-1 a practical screening test that can be drawn at any time without special preparation. An elevated IGF-1 is present in >97% of acromegaly patients, and a low IGF-1 is found in most GH-deficient individuals. However, IGF-1 alone is not diagnostic—dynamic testing (suppression for acromegaly, stimulation for deficiency) is required for confirmation.
The relationship between IGF-1 and cancer is an active area of research. IGF-1 promotes cell growth, proliferation, and survival while inhibiting programmed cell death (apoptosis)—properties that could theoretically promote tumor growth. Epidemiological studies have found associations between higher circulating IGF-1 levels (even within the normal range) and increased risk of certain cancers, including prostate, breast, and colorectal cancer. Patients with acromegaly (chronically elevated IGF-1) have a modestly increased risk of colorectal polyps and cancer. Conversely, individuals with Laron syndrome (GH insensitivity with very low IGF-1) have an extremely low incidence of cancer. However, causality is not established, and IGF-1 levels are not used clinically for cancer risk assessment.
IGF-1 production is highly dependent on both adequate nutrition and healthy liver function. The liver is the primary source of circulating IGF-1, and GH stimulates hepatic IGF-1 production—but only when nutritional status is adequate. Protein intake is particularly important: even with normal GH levels, protein-calorie malnutrition reduces IGF-1 production, creating a state of "GH resistance." This is why IGF-1 is low in anorexia nervosa and kwashiorkor. Liver disease (cirrhosis, hepatitis) directly impairs the liver's ability to produce IGF-1 regardless of GH status. Uncontrolled type 1 diabetes reduces IGF-1 because insulin is needed for hepatic GH receptor expression. These factors must be considered when interpreting IGF-1 results—a low IGF-1 does not always mean GH deficiency.

Related Biomarkers

GHGrowth HormoneGLUGlucoseInsulinInsulin

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.