Serum IGF-1 Level
A blood test measuring insulin-like growth factor 1 concentration, the primary clinical marker for assessing growth hormone activity. Serum IGF-1 is used to diagnose GH deficiency and acromegaly, monitor GH replacement therapy, and assess response to somatostatin analogue treatment.
Technical Context
IGF-1 reference ranges are age- and sex-specific (expressed as μg/L or nmol/L, with SDS/Z-score for comparison to reference population). Peak levels occur during puberty (approximately 300-500 μg/L), declining to approximately 100-200 μg/L in middle age and 50-100 μg/L in elderly. Clinical applications: GHD diagnosis (low IGF-1 supports clinical suspicion but is not sufficient alone — approximately 30-50% of adults with GHD have IGF-1 in the normal range), acromegaly diagnosis and monitoring (elevated IGF-1 confirms GH excess; target normalisation during treatment with somatostatin analogues), GH replacement dose titration (titrate somatropin/somapacitan/somatrogon to maintain IGF-1 in upper half of age-appropriate normal range), and safety monitoring (IGF-1 above normal range during GH therapy increases theoretical cancer risk — though this remains debated). Pre-analytical variables: fasting state, nutritional status, liver function, and oestrogen status affect IGF-1 levels.