GH Stimulation Test
A diagnostic procedure to assess the pituitary gland's ability to produce growth hormone. Various stimuli (including GHRH, glucagon, clonidine, or insulin-induced hypoglycaemia) are used to provoke GH release, which is then measured. Failed stimulation confirms GH deficiency requiring somatropin therapy.
Technical Context
Stimulation tests are required because GH is secreted pulsatily with low baseline levels — a random GH level is uninformative. Standard stimuli: ITT (gold standard — tests hypothalamic-pituitary-adrenal AND somatotroph function), GHRH-arginine (tests pituitary GH reserve directly; arginine suppresses somatostatin, GHRH stimulates; BMI-adjusted cutoffs: BMI<25: GH ≥11, BMI 25-30: GH ≥8, BMI>30: GH ≥4 μg/L), glucagon stimulation test (1mg IM glucagon → GH and cortisol measured over 3-4 hours; cutoff GH ≥3 μg/L), and macimorelin test (oral GHS-R agonist — 0.5mg/kg oral solution → blood GH at 30, 45, 60, 90 minutes; cutoff ≥2.8 μg/L; FDA-approved specifically for adult GHD diagnosis, offering convenience of oral administration). Paediatric GHD requires two failed stimulation tests (to reduce false positive diagnoses). GH stimulation testing establishes the diagnosis that justifies somatropin, somapacitan, or somatrogon therapy.