Growth hormone deficiency - diagnostic testing (insulin tolerance test, IGF-1)
Core concept
- GH is pulsatile - random levels are uninterpretable; a normal random GH neither confirms nor excludes deficiency
- -> diagnosis requires either an integrated marker (IGF-1) or a provocative test
- Axis: hypothalamic GHRH (+) and somatostatin (-) -> pituitary somatotroph -> GH -> hepatic IGF-1 (bound to IGFBP-3 / ALS)
- Ghrelin stimulates via GHS-R1a
- Also stimulated by: hypoglycaemia, arginine, glucagon, sleep (slow-wave), exercise, fasting, dopamine/L-dopa, oestrogen
- Suppressed by: glucose load, free fatty acids, glucocorticoids, obesity, IGF-1 feedback
- The stimulus in the insulin tolerance test is the hypoglycaemia itself, not the insulin - a counter-regulatory stress
3 more sections, plus exam facts
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