Pituitary dynamic tests

Question 1

How can you test for low cortisol levels?

Answer 1

Synacthen: synthetic adrenocorticotropic hormone (ACTH)

-test cortisol levels at 0m/30m/60m

Question 2

How can you test for low growth hormone and cortisol levels?

Answer 2

Insulin stress test (AKA prolonged glucagon test)

• test every 30m for 2-3hrs
• stimulates GH and cortisol secretion

normal cortisol >500
normal GH >7nanograms/L

Question 3

How can you screen for cushings syndrome?

Answer 3

Dexamethasone suppression test: causes -ve feedback on CRH/ACTH = low cortisol

Screening for cushings:
-overnight 1mg suppression test

Diagnose cushings:
-2 day 2mg dexamethasone supression test
(normal is cortisol <50mmol/L 6 hrs after last dose dexamethasone)

Measure plasma ACTH: if this is low = cushings syndrome,if it remains high it is cushings disease

Question 4

How do you test for nephrogenic diabetes insipidus (insensitivity to ADH)?

Answer 4

Water deprivation test

• fluid deprivation then desmopressin administration
• check serum and urine osmolalities for 8hrs then 4hr after giving desmopressin
• if urine/serum osmolarity >2 is normal

Question 5

How do you test for acromegaly?

Answer 5

Glucose tolerance test

• 75g oral glucose, test GH 0, 30, 60, 90, 120mins
• normal = GH suppresses to <0.4nanograms/L after glucose
• in acromegaly GH unchanged/no suppression/paradoxical rise >1nanogram/L after glucose