IGF‑1 as a Biomarker for Growth Hormone Excess and Anabolic Status

Assessment of GH Excess

Elevated IGF‑1, adjusted for age, sex, and Tanner stage, reliably indicates GH excess; the 2024 Nature Reviews Endocrinology consensus guideline gives a strong recommendation based on moderate‑quality evidence. 1
IGF‑1 concentrations rise linearly with GH up to ≈ 4 µg/L and plateau around 10 µg/L in severe GH excess, supporting its use to gauge the magnitude of GH secretion. 2, 4

Reference ranges must be age‑, sex‑, and pubertal‑stage specific; marginal elevations during the adolescent growth spurt require cautious interpretation. 1, 3, 5
Conditions that can produce falsely low IGF‑1 despite GH excess include severe hypothyroidism, malnutrition or severe infection, and oral estrogen therapy. 7, 3, 4
Conditions that can cause falsely elevated IGF‑1 without GH excess include poorly controlled diabetes mellitus and hepatic and/or renal failure. 3

Inter‑assay variability is substantial; laboratories should establish local, Tanner‑stage‑matched, sex‑matched, and age‑matched reference intervals for each IGF‑1 assay. 1, 3
Assay‑specific reference ranges must be used; ignoring them can lead to misinterpretation. 1

For suspected GH excess, measure IGF‑1 using appropriate reference ranges before further work‑up. 1
If IGF‑1 is elevated, interpret the result together with height velocity, pubertal stage, and bone age to confirm clinical relevance. 1, 5
In confirmed GH excess, both GH and IGF‑1 should be measured at baseline and during follow‑up to track disease activity and treatment response. 2, 4
Before attributing an elevated IGF‑1 to GH excess, rule out confounding factors such as uncontrolled diabetes, renal or hepatic dysfunction, and medications that affect IGF‑1 production. 1
During recombinant GH therapy, IGF‑1 should be monitored at least twice yearly; dosing is adjusted to keep IGF‑1 within the physiologic range, improving safety and growth prediction. 7

Never interpret IGF‑1 in isolation; always integrate clinical phenotype, growth parameters, and potential confounders. 1, 5
A single elevated IGF‑1 should not be used to diagnose acromegaly in adolescents, as physiologic puberty‑related rises are common. 1, 8
Assay‑specific reference ranges must be applied; failure to do so can produce erroneous conclusions. 1