Unit Converter
IGF-1 – Insulin-like growth factor 1 (Somatomedin C)
Synonyms
- IGF-1
- Insulin-like Growth Factor 1
- Somatomedin-C
- Growth-promoting peptide
- SM-C
- Serum IGF-1
Units of Measurement
- nmol/L
- µg/L
- µg/dL
- µg/100 mL
- µg%
- ng/mL
Key Conversions
(Molecular Weight ≈ 7649 Da ≈ 7.65 kDa)
1 ng/mL = 1 µg/L
1 µg/L ≈ 0.13 nmol/L
1 nmol/L ≈ 7.65 µg/L
1 µg/dL = 10 µg/L = 10 ng/mL
µg/100 mL = µg/dL = µg%
Description
IGF-1 is a polypeptide hormone mainly produced by the liver in response to growth hormone (GH) stimulation.
KEY PROPERTIES:
- Stable and non-pulsatile
- Reflects integrated GH secretion
- Age-dependent
- Strongly influenced by nutrition, liver function, and chronic illness
IGF-1 binds to IGF-binding proteins (IGFBPs), especially IGFBP-3, forming IGF-1/IGFBP-3/ALS complexes circulating in blood.
Physiological Role
IGF-1 mediates MANY actions of GH:
1. Linear Growth
- Promotes epiphyseal growth plate expansion
- Drives chondrocyte proliferation
2. Anabolism
- Protein synthesis
- Muscle growth
- Organ development
3. Metabolic Effects
- Insulin-like glucose uptake
- Lipid metabolism
4. Cell Survival & Repair
- Anti-apoptotic effects
- Tissue regeneration
Clinical Significance
HIGH IGF-1
1. Acromegaly (Adults) / Gigantism (Children)
- PRIMARY screening test for acromegaly
- Elevated IGF-1 in >95% of cases
- Must be confirmed with GH suppression test (OGTT)
Features:
- Enlarged hands/feet
- Jaw prognathism
- Soft-tissue overgrowth
- Hypertension
- DM / insulin resistance
2. Puberty
Physiological peak.
3. High Protein Intake
Nutritional stimulation.
4. Pregnancy
Mild physiologic increase.
5. Rare Tumors
- IGF-1–secreting tumors (very rare)
- Some Ewing sarcomas and Wilms tumors (rare associations)
LOW IGF-1
1. Growth Hormone Deficiency (GHD)
Best screening test for:
- Pediatric GHD
- Adult GHD
Low IGF-1 + failed stimulation test = GH deficiency.
2. Chronic Systemic Disease
- Malnutrition
- Chronic liver disease
- CKD
- Inflammatory diseases
- Celiac disease
3. Hypothyroidism
Reduces IGF-1 production.
4. Diabetes / Poor Glycemic Control
Low–normal IGF-1.
5. Aging
Levels decline with age.
Reference Intervals
Values vary widely; always use age-adjusted z-score.
Typical Adult Values:
- 20–40 years: 120–360 µg/L
- 40–60 years: 80–250 µg/L
- >60 years: 50–200 µg/L
Children & Adolescents:
- Peaks during puberty: 300–1200 µg/L
- Lowest in toddlers and elderly.
Acromegaly Cutoffs
- IGF-1 above age-adjusted upper limit → suspect acromegaly
- Confirm with OGTT GH suppression (<1 ng/mL or <0.4 ng/mL ultrasensitive)
GH Deficiency
- IGF-1 below -2 SD for age
- Confirm with GH stimulation testing.
Diagnostic Uses
1. Screening for Acromegaly
IGF-1 elevated → do GH suppression test.
2. Diagnosis of Growth Hormone Deficiency
Low IGF-1 + failed stimulation test.
3. Monitoring GH Therapy
In both children and adults:
- Titrate GH dose using IGF-1 target range (normal for age).
4. Pediatric Growth Disorders
- Short stature
- Constitutional delay
- Poor weight/height velocity
5. Liver Disease / Nutrition Assessment
IGF-1 reflects:
- Liver synthetic function
- Protein nutrition status
- Chronic illness burden
Analytical Notes
- Fasting not required
- Serum or plasma acceptable
- MUST interpret with age- and sex-matched reference ranges
- Biotin supplements may interfere with immunoassays
- IGF-1 stable after collection; minimal pre-analytical issues
- Use same assay for serial monitoring
Clinical Pearls
- IGF-1 is far more stable than GH → ideal for screening.
- Low IGF-1 does NOT necessarily mean GH deficiency - check:
- Liver disease
- Malnutrition
- Hypothyroidism
- Chronic inflammation
- Liver disease
- GH excess rarely shows normal IGF-1 (high sensitivity).
- In acromegaly monitoring, IGF-1 normalization = biochemical control.
- IGF-1 is a better marker than GH for assessing adequacy of GH therapy.
Interesting Fact
Although GH pulses occur every 2–3 hours, IGF-1 remains stable throughout the day, which is why it revolutionized acromegaly diagnosis when introduced.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - IGF-1.
- Endocrine Society Guidelines - Acromegaly & GH Deficiency.
- Pediatric Endocrine Society - GH/IGF-1 Testing.
- Mayo Clinic Laboratories - IGF-1.
- ARUP Consult - GH & IGF-1 Interpretation.
- MedlinePlus / NIH - IGF-1 Test.