Y2 ENDOCRINE TESTS Flashcards
to investigate if adrenal insufficiency?
short synacthen test
how do you perform a short synacthen test?
- measure plasma cortisol
before test.
–> IV/IM ACTH
- measure plasma 30 minutes after.
what is a normal ACTH baseline?
> 250nmol/L
what should cortisol be normally after ACTH injection
> 550nmol/L
what will happen in the synacthen test if the patient has adrenal insufficiency?
cortisol will remain low despite ACTH injection.
Should not rise above >550nmol/L after 30 min or increase by >200nmol/L.
what will happen to levels in the synacthen test if the patient has adrenal insufficiency?
- very high ACTH.
- low cortisol.
- high renin.
- low aldosterone.
how do you diagnose cushing’s?
- overnight dexamethasone suppression test.
- 24hour urinary free cortisol.
- late night salivary cortisol.
- low dose dexamethasone suppression test.
repeat to confirm.
what results of an overnight dexamethasone test will be seen in Cushing’s?
plasma cortisol >50nmol/L.
what results of a 24 hour urine free cortisol will be seen in Cushing’s?
elevation
what results of a low dose dexamethasone suppression test would indicate cushing’s?
no suppression.
if there is suppression it suggests another cause e.g. depression, obesity, alcohol abuse.
following a failure of cortisol to suppress after a low dose dexamethasone suppression test, what would be the next step?
imaging/investigation for pituitary adenoma or ectopic source of ACTH.
test to diagnose primary aldosteronism?
aldosteron to renin ratio.
if suspicion of primary aldosteronism and ARR is raised, what is the next step?
saline suppression test
what confirms primary aldosteronism?
failure of plasma aldosterone to suppress by >50% with 2 litres of saline
how do you confirm subtype of primary aldosteronism?
- adrenal CT to check for adenoma or bilateral adrenal hyperplasia.
?- adrenal vein sampling to confirm adenoma is true source of excess aldosterone - only sometimes check?
how do you diagnose congenital adrenal hyperplasia?
basal or stimulated 17-OH progesterone.
how do you investigate phaeochromocytoma initially?
- urinary 24 hour catecholamines or metanephrins.
- plasma catecholamine (ideally when symptomatic).
note it is episodic catecholamine secretion therefore urine and plasma levels may be normal.
how do you confirm phaeochromocytoma once catecholamine excess has been established?
MRI scan (abdo. or whole body).
- MIBG
- PET
when might phaeochromocytoma levels of catecholamine be low?
- if malignant or extra-adrenal as they are less efficient at catecholamine synthesis.
- catecholamine excretion is episodic.
investigation of hypercalcaemia?
PTH
Low/normal albumin +
- suppressed PTH
- high phosphate
suggests?
bone pathology
Low/normal albumin +
- high/normal PTH
- low/normal phosphate
- reduced urine Ca2+ suggests?
familial hypocalciuric hypercalcaemia (FHH)
Low/normal albumin +
- high/normal PTH
- low/normal phosphate
- increased urine Ca2+ suggests?
primary or tertiary hyperparathyroidism
- hypercalcaemia
- raised albumin
- raised urea
suggests?
dehydration
