Insulin-like Growth Factor 1 (IGF-1)
IGF-1 is the liver-produced messenger that does most of growth hormone's downstream work. It's far more stable in blood than GH itself, making it the practical screening test for acromegaly and adult GH deficiency.
What it measures
IGF-1 (also called somatomedin C) is made by the liver in response to pulses of pituitary growth hormone (GH). Because GH pulses are short and erratic, a single random GH is rarely interpretable; IGF-1 averages those pulses over hours and is therefore the screening test of choice for both GH excess (acromegaly) and adult-onset GH deficiency. IGF-1 also peaks in adolescence and declines steadily with age — so reference ranges must be matched to age and sex. IGF-1 mediates GH's effects on bone, muscle, fat distribution and metabolism.
What a high value can mean
- Acromegaly / gigantism — pituitary adenoma; IGF-1 above age-matched range, often paired with insulin resistance.
- Puberty / pregnancy — physiological surge.
- Hyperthyroidism, obesity (mild) — modest elevation.
- Exogenous GH therapy — therapeutic monitoring above the normal range warrants dose reduction.
What a low value can mean
- Adult growth hormone deficiency — pituitary disease (surgery, radiation, tumour); paired with reduced muscle mass, central obesity, low mood.
- Malnutrition / anorexia nervosa — IGF-1 falls before albumin does.
- Severe hypothyroidism, poorly controlled diabetes — modest reduction.
- Hepatic failure — impaired synthesis.
- Normal ageing — values in 70s match what would be 'low' in 20s.
When to discuss with a doctor
IGF-1 outside age-matched range warrants endocrinology follow-up: high → screen for pituitary adenoma (MRI + oral glucose suppression test); low → assess pituitary function (GH stimulation test). Self-supplementation with GH or IGF-1 is dangerous and unregulated. Mediora.AI surfaces the value against the age band; treatment changes belong with an endocrinologist.