Adult Growth Hormone Deficiency (AGHD)

Adult growth hormone deficiency is a defined endocrine diagnosis, not a description of low-normal hormone levels. It follows structural or treatment-related pituitary damage, most often a pituitary or parasellar tumour and its surgery or radiotherapy, and less commonly traumatic brain injury or childhood-onset deficiency persisting into adult life. The phenotype is real but non-specific: increased fat mass with a visceral distribution, reduced lean mass and exercise capacity, low bone mineral density, an atherogenic lipid profile and impaired quality of life.

Because secretion is pulsatile, diagnosis requires provocation rather than a random measurement. The insulin tolerance test remains the reference standard, with a peak below roughly 3 micrograms per litre taken as severe adult deficiency, and the glucagon test substitutes where hypoglycaemia is contraindicated. Macimorelin, an orally active ghrelin-receptor agonist, was approved by the FDA in 2017 and the EMA in 2018 with its own validated cut-off. Somatropin has been approved for adult deficiency since the mid-1990s, titrated to bring IGF-1 into the reference range rather than to a weight-based target.

The diagnostic boundary matters because it separates replacing an absent hormone from supplementing a normal one, and only the former is an approved use. It also sets the monitoring frame, with response judged on body composition, lipids, bone density and symptom scores while IGF-1 steers dose rather than proving benefit.

The routine misuse is a diagnosis asserted from symptoms plus a single IGF-1 result. IGF-1 has poor sensitivity here: a substantial share of adults with test-confirmed organic deficiency have IGF-1 inside the reference range, while a low IGF-1 is far more often explained by age, adiposity, liver disease or undernutrition than by pituitary failure.