Insulin-like growth factor 1
End hormone or mediator · IGF-1 IGFBP-3 Growth plate
IGF-1 carries most of growth hormone's growth effect at the epiphyseal plate and feeds back on both the somatotroph and hypothalamic somatostatin. It is the screening test for GH excess and deficiency.
Traced from the start
Detail
- Growth
- Stimulates chondrocyte proliferation at the growth plate; after fusion, GH excess thickens bone and soft tissue instead of lengthening it
- Confirming excess
- Raised age-matched IGF-1 plus failure of GH to fall below 1 microgram/L (0.4 with ultrasensitive assays) during a 75 g oral glucose tolerance test
- Metabolic
- IGF-1 has weak insulin-like activity while GH itself opposes insulin, which is why acromegaly causes diabetes
When it goes wrong
Acromegaly confirmed on IGF-1 and OGTT
Transsphenoidal surgery is first line, with somatostatin analogues or pegvisomant (a GH receptor antagonist) if not cured; screen for colorectal polyps, sleep apnoea and cardiomyopathy
Childhood growth hormone deficiency
Growth velocity falls across the centiles with preserved weight and a delayed bone age; confirm with a stimulation test before treating
Practise this structure
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