Insulin-like Growth Factor (IGF-1)

Insulin-like Growth Factor 1 (IGF-1) is a hormone produced mainly by the liver in response to growth hormone (GH) from the pituitary gland. While growth hormone itself is difficult to measure reliably because it’s released in pulses throughout the day, IGF-1 remains stable in the blood, making it an excellent indicator of overall growth hormone activity. Think of IGF-1 as the “report card” for growth hormone — it tells you how much GH effect the body is actually experiencing.

Why does this matter? IGF-1 testing helps diagnose conditions of growth hormone excess or deficiency. In children, it evaluates short stature and growth failure. In adults, it can identify growth hormone deficiency (causing fatigue, decreased muscle mass, and reduced quality of life) or acromegaly (growth hormone excess causing enlarged features and serious health complications). Because growth hormone problems develop gradually, IGF-1 provides an objective measure that can catch these conditions before they become obvious.

Order Your IGF-1 Test

---

Key Benefits of Testing

IGF-1 provides a stable, reliable measure of growth hormone status. Unlike GH itself, which fluctuates dramatically throughout the day (making random measurements unreliable), IGF-1 remains relatively constant and reflects average GH activity over time. A single blood draw gives meaningful information.

Testing is essential for diagnosing and monitoring pituitary disorders. Both growth hormone deficiency and excess have significant health consequences that are treatable once identified. IGF-1 is also used to monitor response to GH therapy, ensuring appropriate dosing.

---

What Does This Test Measure?

The IGF-1 test measures the concentration of Insulin-like Growth Factor 1 in blood. IGF-1 is a peptide hormone structurally similar to insulin (hence the name). It’s produced primarily by the liver when stimulated by growth hormone, though other tissues also produce it in smaller amounts.

How IGF-1 Works

The growth hormone axis works like this: the pituitary gland releases growth hormone in pulses, mainly during sleep and after exercise. GH travels to the liver and stimulates IGF-1 production. IGF-1 then circulates in the blood (mostly bound to carrier proteins called IGFBPs) and mediates most of growth hormone’s effects — promoting growth in children, maintaining muscle and bone in adults, and influencing metabolism throughout life.

IGF-1 also provides negative feedback to the pituitary, helping regulate GH secretion. When IGF-1 is high, the pituitary reduces GH output. When IGF-1 is low, GH secretion increases (in a healthy system).

Why IGF-1 Instead of Growth Hormone

Growth hormone is released in pulses — levels can vary 10-fold or more within hours. A random GH measurement might catch a peak, a trough, or anything in between, making interpretation nearly impossible. IGF-1 integrates GH activity over time and remains stable throughout the day. This makes IGF-1 the preferred screening test for growth hormone disorders.

IGF-1 Through Life

IGF-1 levels change predictably with age. They’re relatively low in early childhood, rise during puberty (driving the adolescent growth spurt), peak in late adolescence or early adulthood, then gradually decline with age. Results must always be interpreted against age-appropriate reference ranges.

---

Why This Test Matters

Evaluating Growth in Children

Investigates short stature. When a child is significantly shorter than expected or growing too slowly, IGF-1 helps determine whether growth hormone deficiency might be responsible. Low IGF-1 suggests inadequate GH activity and warrants further evaluation.

Screens for growth hormone deficiency. GH deficiency can be congenital or acquired (from pituitary tumors, radiation, trauma). Early diagnosis allows treatment with growth hormone therapy, which can significantly improve final adult height when started early.

Diagnosing Adult Growth Hormone Disorders

Identifies adult GH deficiency. Growth hormone remains important throughout life. Adult GH deficiency — from pituitary disease, tumors, surgery, or radiation — causes reduced muscle mass, increased body fat (especially abdominal), decreased bone density, fatigue, and reduced quality of life. Low IGF-1 suggests this diagnosis.

GH Deficiency: Children vs Adults

Feature	Children	Adults
Main symptom	Short stature, slow growth velocity	Fatigue, reduced quality of life
Body composition	Increased body fat, young face for age	↓ muscle mass, ↑ abdominal fat
Bone effects	Delayed bone age	Decreased bone density, fracture risk
Treatment goal	Maximize final adult height	Improve energy, body composition, QoL

Screens for acromegaly. Acromegaly is caused by a pituitary tumor that secretes excess growth hormone. The disease develops slowly — over years, patients develop enlarged hands, feet, and facial features; joint pain; and serious complications including diabetes, hypertension, and heart disease. IGF-1 is the best screening test because it’s elevated even when random GH levels appear normal.

Monitoring Treatment

Guides GH replacement therapy. Children and adults receiving growth hormone therapy need regular IGF-1 monitoring to ensure doses achieve appropriate levels — high enough for benefit but not excessive.

Tracks acromegaly treatment. After surgery, radiation, or medication for acromegaly, IGF-1 monitoring shows whether treatment has normalized GH activity. Persistent elevation indicates need for additional therapy.

Value of Early and Proactive Testing

Growth hormone disorders develop gradually — often over years — making them easy to miss without testing. Children with GH deficiency may simply seem “small for their age” without dramatic symptoms. Adults often attribute fatigue and body composition changes to stress or normal aging. Acromegaly progresses so slowly that patients and families don’t notice the gradual changes in appearance.

Testing IGF-1 when early suspicion exists provides several advantages. In children, earlier diagnosis means earlier treatment and better final height outcomes — every year of delayed diagnosis is lost growth potential. In adults with pituitary history (tumor, surgery, radiation), baseline IGF-1 testing can catch developing GH deficiency before significant symptoms accumulate. For acromegaly, earlier detection means smaller tumors, easier surgery, and fewer years of complications like diabetes and heart disease. IGF-1 testing transforms vague concerns into actionable diagnoses.

---

What Can Affect IGF-1 Levels?

Causes of Low IGF-1

• Growth hormone deficiency — pituitary or hypothalamic causes
• Pituitary tumors, surgery, or radiation affecting GH production
• Malnutrition and eating disorders — IGF-1 falls with inadequate nutrition
• Liver disease — impaired hepatic IGF-1 production
• Poorly controlled diabetes
• Hypothyroidism
• Chronic illness and inflammatory conditions
• Laron syndrome — GH receptor deficiency (rare)
• Aging — natural decline
• Estrogen therapy (oral) — decreases IGF-1

Causes of High IGF-1

• Acromegaly — GH-secreting pituitary tumor
• Gigantism — excess GH before growth plates close (in children)
• Puberty — normal physiological increase
• Pregnancy
• Obesity (sometimes mildly elevated)
• High protein intake
• Exogenous growth hormone use (therapeutic or illicit)

Factors Affecting Interpretation

Age is the most important factor — IGF-1 must be compared to age-matched reference ranges. Nutritional status matters significantly; fasting or malnutrition lowers IGF-1 regardless of GH status. Liver function affects production — severe liver disease can cause low IGF-1 even with normal GH. Certain medications, chronic illness, and poorly controlled diabetes can all affect levels.

---

When Should You Get Tested?

In Children

Short stature or poor growth velocity: Height significantly below expected, crossing percentile lines downward, or growing less than expected for age.

Delayed puberty: May be associated with GH or other pituitary hormone deficiencies.

History of pituitary/brain problems: Tumors, radiation, trauma, or surgery affecting the pituitary region.

Symptoms suggesting GH deficiency: Delayed bone age, increased body fat, young facial appearance for age.

In Adults

Symptoms suggesting GH deficiency: Fatigue, decreased muscle mass, increased abdominal fat, reduced exercise capacity, poor concentration, reduced quality of life — especially with history of pituitary disease.

Known pituitary disease: Pituitary tumors, surgery, radiation, or other conditions affecting the pituitary.

Features suggesting acromegaly: Enlarging hands or feet (rings or shoes no longer fit), coarsening facial features, prominent jaw, joint pain, excessive sweating, sleep apnea, new-onset diabetes or hypertension.

Monitoring GH therapy: Regular testing ensures appropriate dosing.

Monitoring acromegaly treatment: Confirms disease control after surgery, radiation, or medication.

Order Your Test

---

Understanding Your Results

IGF-1 interpretation requires comparison to age-appropriate reference ranges. A level that’s normal for a 60-year-old might indicate deficiency in a teenager.

IGF-1 Interpretation at a Glance

IGF-1 Level	Suggests	Next Steps
Low for age	GH deficiency, malnutrition, liver disease, chronic illness	Rule out nutritional/illness causes → GH stimulation testing if indicated
Normal for age	Adequate GH activity	GH deficiency unlikely (though doesn’t 100% exclude mild cases)
High for age	Acromegaly, gigantism, or GH therapy	Oral glucose tolerance test + pituitary MRI

Low IGF-1

Low IGF-1 for age suggests reduced growth hormone activity. In children with poor growth, this supports possible GH deficiency warranting further evaluation (GH stimulation testing). In adults with compatible symptoms and history (pituitary disease, surgery, radiation), low IGF-1 suggests adult GH deficiency.

However, low IGF-1 isn’t specific to GH deficiency. Malnutrition, liver disease, poorly controlled diabetes, and chronic illness can all lower IGF-1. Clinical context matters for interpretation.

Normal IGF-1

Normal IGF-1 generally indicates adequate GH activity, though it doesn’t completely rule out mild GH deficiency in some cases. If clinical suspicion remains high despite normal IGF-1, GH stimulation testing may still be warranted.

High IGF-1

Elevated IGF-1 for age raises concern for GH excess. In adults, this suggests acromegaly — further evaluation includes oral glucose tolerance test (GH should suppress with glucose loading but fails to in acromegaly) and pituitary MRI looking for adenoma. In children/adolescents before growth plate closure, GH excess causes gigantism.

Mildly elevated IGF-1 can occur with puberty, pregnancy, or high protein intake. Significantly elevated IGF-1 with compatible symptoms strongly suggests pathological GH excess.

---

What to Do About Abnormal Results

For Low IGF-1

Evaluate nutritional status. Malnutrition and eating disorders lower IGF-1. If nutritional deficiency is present, addressing it may normalize IGF-1.

Check other factors. Liver function, thyroid function, diabetes control — treat reversible causes.

Consider GH deficiency evaluation. If clinical suspicion exists (poor growth in children, symptoms plus pituitary history in adults) and other causes are excluded, GH stimulation testing confirms or rules out GH deficiency. This involves measuring GH response to provocative stimuli (insulin, arginine, glucagon, etc.).

Treatment for GH deficiency. Confirmed GH deficiency is treated with recombinant human growth hormone. In children, this improves growth and final height. In adults, it improves body composition, bone density, energy, and quality of life.

For High IGF-1

Confirm the elevation. Repeat testing may be appropriate if the elevation is mild or unexpected.

Evaluate for acromegaly. Oral glucose tolerance test (OGTT) with GH measurement — normally, GH suppresses after glucose load, but fails to suppress in acromegaly. Pituitary MRI looks for adenoma.

Treatment for acromegaly. Usually begins with transsphenoidal surgery to remove the pituitary tumor. If surgery doesn’t achieve cure, medication (somatostatin analogs, GH receptor antagonists, dopamine agonists) and/or radiation therapy may be needed. IGF-1 monitoring tracks treatment success.

---

Related Health Conditions

Growth Hormone Deficiency (Pediatric)

Children with GH deficiency grow slowly and have short stature. The condition may be congenital or acquired from tumors, radiation, or trauma. Low IGF-1 supports the diagnosis. Treatment with growth hormone replacement can significantly improve growth and final adult height when started early.

Adult Growth Hormone Deficiency

Adults can develop GH deficiency from pituitary tumors, surgery, radiation, or traumatic brain injury. Symptoms include fatigue, reduced muscle mass, increased body fat, decreased bone density, and impaired quality of life. Low IGF-1 suggests the diagnosis. GH replacement therapy improves body composition, energy, and wellbeing.

Acromegaly

Acromegaly results from a GH-secreting pituitary adenoma causing chronic GH excess. Features include enlarged hands and feet, coarsened facial features, joint pain, and serious complications (diabetes, hypertension, heart disease, sleep apnea). IGF-1 is the primary screening test. Treatment involves surgery, medication, and sometimes radiation.

Gigantism

When GH excess occurs before growth plates close (childhood/adolescence), it causes excessive linear growth — gigantism. Children grow extremely tall. IGF-1 is elevated. Early treatment prevents extreme height and complications.

Pituitary Tumors

Pituitary adenomas can secrete excess GH (causing acromegaly) or compress normal pituitary tissue (causing hormone deficiencies including GH deficiency). IGF-1 helps assess GH status in patients with known or suspected pituitary tumors.

Short Stature

Short stature has many causes — familial, constitutional, nutritional, chronic disease, hormonal, and genetic syndromes. IGF-1 testing helps determine whether GH deficiency contributes. Normal IGF-1 suggests other causes should be explored.

---

Related Biomarkers Often Tested Together

Growth Hormone — While random GH is unreliable, GH testing during stimulation tests or glucose suppression tests confirms diagnosis.

IGFBP-3 — IGF binding protein-3 is sometimes tested alongside IGF-1; both are GH-dependent and together provide additional information.

Pituitary hormones (FSH, LH, TSH, ACTH, Prolactin) — When pituitary disease is suspected, comprehensive pituitary function testing assesses multiple hormones.

Glucose — Used in oral glucose tolerance test for acromegaly diagnosis; also monitors diabetes risk in acromegaly.

Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.