IGF-1 Test: Growth Hormone Marker, High/Low Levels & Symptoms

IGF-1 Test: Role, High/Low Levels, Growth Disorders & Complete Medical Guide

What Is Insulin-Like Growth Factor 1 (IGF-1)?

Insulin-Like Growth Factor 1 (IGF-1), also known as Somatomedin C, is a protein hormone that resembles insulin in structure and function. IGF-1 is strongly regulated by Growth Hormone (GH) and is one of the most important hormones responsible for physical growth in children and metabolic health in adults.

Unlike GH—which fluctuates throughout the day—IGF-1 remains stable in the bloodstream. This stability makes IGF-1 one of the most reliable tests for evaluating growth hormone activity and diagnosing disorders related to abnormal GH production.

Doctors commonly order IGF-1 testing to evaluate:

Growth failure or short stature in children
Suspected gigantism or acromegaly
Pituitary gland disorders
Poor growth during puberty
Nutritional or metabolic problems
Liver health and chronic illness

Because IGF-1 reflects long-term GH levels, it is essential in both endocrine and growth-related evaluations.

Where Is IGF-1 Produced in the Body?

IGF-1 is produced in several tissues, but its primary source is the liver.

Main production site

Liver — stimulated directly by Growth Hormone

Other tissues that produce smaller amounts

Muscles
Bones
Cartilage
Fat tissue
Multiple organs for local growth and repair

While local tissues use IGF-1 for cell repair and regeneration, the circulating (blood) IGF-1 that doctors measure comes mostly from the liver.

Main Functions and Importance of IGF-1

1. Supports Bone Growth

IGF-1 plays a major role in childhood growth. It increases bone length, density, and strength. Children with low IGF-1 often grow more slowly and may have shorter adult height without treatment.

2. Helps Build and Repair Muscle

IGF-1 promotes:

Protein synthesis
Muscle development
Tissue repair after injury
Recovery from physical stress

This function is important for both athletic performance and overall physical strength.

3. Controls Metabolism

IGF-1 affects multiple metabolic pathways by helping the body regulate:

Glucose uptake
Fat burning
Energy production

Abnormal IGF-1 levels can disrupt metabolism and lead to fatigue, weight issues, and muscle weakness.

4. Supports Cell Growth and Survival

IGF-1 is essential for:

Healthy cell division
Tissue regeneration
Maintaining organ function

It contributes to skin repair, nerve protection, and balanced aging.

5. Stable Marker for GH Activity

Because GH is released in pulses, a single GH measurement can be misleading. IGF-1 stays stable throughout the day and is used to:

Detect GH deficiency
Monitor GH replacement therapy
Diagnose GH excess (acromegaly or gigantism)

This makes IGF-1 one of the most valuable tests in endocrinology.

Causes of Low IGF-1 Levels

1. Growth Hormone Deficiency

This is the most common cause in both children and adults. It may be due to:

Pituitary gland problems
Genetic disorders
Tumors
Surgery or radiation near the brain

2. Genetic Growth Disorders

Certain inherited conditions affect the GH-IGF-1 axis, resulting in low levels.

3. Malnutrition or Chronic Illness

Protein deficiency, calorie restriction, or long-term illness reduces IGF-1 production because the body prioritizes survival over growth.

4. Hypothyroidism

Low thyroid hormones slow metabolism and growth, reducing IGF-1 levels.

5. Liver Disease

Because IGF-1 is made in the liver, cirrhosis and hepatitis can severely reduce production.

6. Normal Aging

Levels naturally decline with age, contributing to muscle loss and reduced bone strength.

Symptoms of Low IGF-1 Levels

In Children

Short height
Slow growth rate
Delayed puberty
Weaker bones
Low muscle mass
Poor energy

In Adults

Fatigue
Increased body fat
Reduced muscle mass
Thin or weak bones
Decreased exercise tolerance
Poor mood or motivation

In Older Adults

Frailty
Slow healing
General weakness
Higher risk of falls

Low IGF-1 itself does not cause symptoms—symptoms arise from the underlying cause such as GH deficiency or chronic illness.

Causes of High IGF-1 Levels

1. Growth Hormone Excess

Excess GH from the pituitary gland is the most common cause.

2. Pituitary Tumors

A GH-secreting adenoma produces high IGF-1 and leads to:

Gigantism in children
Acromegaly in adults

These tumors may also press on surrounding brain structures.

3. High Protein Intake or Supplements

Temporary increases may occur after large protein meals or certain supplements.

4. Rare Cancers

Some tumors outside the pituitary may produce GH or IGF-1.

Symptoms of High IGF-1 Levels

In Children: Gigantism

Rapid height increase
Exceptionally tall growth
Enlarged hands, feet, and facial bones

In Adults: Acromegaly

Enlarged jaw, nose, or forehead
Thickened skin
Widened fingers and toes
Joint pain
Excessive sweating
Deepening voice

Symptoms of Pituitary Tumor

Headaches
Blurred or double vision
Reduced peripheral vision

Long-Term Risks

Chronic high IGF-1 levels may increase long-term risk of:

Colon cancer
Prostate cancer
Breast cancer

Reference Ranges

Ranges vary by age, sex, and puberty stage.

Approximate examples:

Children (10–12 years)

100–600 ng/mL

Adults (20–40 years)

150–350 ng/mL

Older Adults (>60 years)

50–200 ng/mL

Interpretation should always be based on the laboratory’s reference values.

Sample Type

Blood sample (serum)

Test Preparation

No fasting required
Avoid excessive protein intake before testing
Inform the doctor about GH therapy
Thyroid, liver, and nutritional tests may be recommended
For acromegaly evaluation, an OGTT (Oral Glucose Tolerance Test) may be needed

When to Consult a Doctor

Children

Slow growth or shorter height compared to peers
Very rapid or excessive growth
Delayed or early puberty
Signs of GH deficiency

Adults

Enlarging hands or feet
Change in face shape
Persistent fatigue
Unexplained weight gain
Joint stiffness
Vision problems or chronic headaches

Anyone With

Known pituitary disorders
Chronic liver disease
Abnormal GH treatment response

Early evaluation helps prevent complications and ensures proper treatment.

Important Word Explanations

Growth Hormone (GH): Hormone responsible for growth and metabolism.
Acromegaly: GH excess in adults causing enlarged bones and tissues.
Gigantism: GH excess in children causing extremely tall growth.
Adenoma: Benign tumor that produces hormones.
Somatomedin C: Another name for IGF-1.
Protein Synthesis: Process of building muscle and body tissues.

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