IGF-1 (Insulin-like Growth Factor 1)
IGF-1 is produced mainly by the liver in response to growth hormone (GH). Unlike GH itself, which is pulsatile and difficult to measure, IGF-1 is stable through the day and gives a reliable picture of average GH activity. IGF-1 is the primary screening test for acromegaly (GH excess, usually from a pituitary adenoma) and for GH deficiency in children and adults. Levels vary with age — peaking in adolescence and declining through adult life.
Reference Ranges
Male
90 – 360
ng/mL
Female
90 – 360
ng/mL
Child
90 – 480
ng/mL
Peaks in adolescence, lower in young children
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low IGF-1 in children with poor growth suggests GH deficiency — requires GH stimulation testing for confirmation. In adults, low IGF-1 may reflect GH deficiency from pituitary disease, malnutrition, hypothyroidism, poorly controlled diabetes, or liver disease. Adult GH deficiency rarely needs replacement outside specific pituitary diseases. Age-adjusted reference ranges are essential — 'normal' varies a lot by age.
What High Levels Mean
Elevated IGF-1 for age strongly suggests acromegaly (in adults) or gigantism (in children) — usually due to a GH-secreting pituitary adenoma. Symptoms: enlarged hands, feet, and facial features; joint pain; sweating; deepening voice; hypertension; diabetes; sleep apnea. Oral glucose tolerance test with GH sampling confirms, and pituitary MRI identifies the adenoma. Surgery is first-line treatment.
Frequently Asked Questions
Why is IGF-1 used instead of growth hormone?
GH is released in pulses throughout the day with long periods of near-zero levels between peaks — so a random GH measurement is almost useless. IGF-1 integrates average GH activity over days and is stable, requires no fasting, and is collected at any time. For definitive diagnosis, dynamic testing (glucose-suppressed GH for acromegaly, GH stimulation for deficiency) is still needed.
Does IGF-1 decline with age?
Yes. IGF-1 peaks in adolescence (puberty-related GH surge), is high in young adults, and declines steadily through middle and older age. Age-specific reference ranges are essential — what is 'low' at age 30 may be normal at age 70. Always compare to the age-appropriate range on your report.
When should acromegaly be suspected?
Gradual changes in hand and foot size (rings no longer fit, shoe size increasing), facial coarsening (brow, jaw, nose, lips), new joint pains, sleep apnea, hypertension, diabetes, and excessive sweating — especially if all appear together in adulthood. Acromegaly is often diagnosed late because changes are gradual — comparing with old photographs often makes the progression obvious.
Related Hormones tests
See all →Insulin (Fasting / Random)
Pancreatic hormone that controls blood sugar.
µIU/mLHormonesHOMA-IR (Insulin Resistance Index)
Calculated index that estimates insulin resistance.
indexHormonesBeta-hCG (Human Chorionic Gonadotropin)
Pregnancy hormone — also a tumor marker for certain cancers.
mIU/mLHormonesSex Hormone Binding Globulin (SHBG)
Protein that binds sex hormones in blood, controlling their availability.
nmol/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
Read Full Medical Disclaimer →