Hormone Dynamic Test

What tests are used if Cushings is suspected

Overnight, low dose, high dose dexamethasone

What is overnight dexamethasone test

Give 1mg DEX at night → Blood draw 9hrs later → Cortisol should DROP → If high = autonomous secretion → Do high dose

What is low dose dexamethasone test

Take low dose DEX → If cortisol drops on day 3 → Confirm Cushing’s syndrome

What is high dose dexamethasone test

Give high dose DEX → Cortisol low is Cushing DISEASE (pituitary tumor), if high test ACTH

High dose DEX shows high cortisol + low ACTH what is the cause of hypercortisol

ACTH independent tumor → Secretion of cortisol without ACTH production

High dose DEX shows high cortisol + high ACTH what is the cause of hypercortisol

Ectopic tumor that is making ACTH → Leads to cortisol production

Adrenal insufficiency tests

Cosyntropin test, desmopressin test, insulin tolerance

What is Cosyntropin test

Diff primary from secondary AI; draw baseline ACTH and cortisol → Give cosyntropin (synthetic ACTH) → Measure cortisol again

Low cortisol after cosyntropin administration means what

Adrenal gland damage → Cannot respond to ACTH → PRIMARY AI

Mild/blunted cortisol rise after cosyntropin administration means what

LACK of endogenous ACTH → Adrenal atrophy → caused by pituitary problem → SECONDARY AI

What is desmopressin test

Used to diff causes of DI (nephrogenic or central); Give dDDAVP= synthetic ADH after water deprivation → Look at urine Osm

Urine Osm increase after desmopressin and dilute in fluid deprivation

Central DI (pituitary cannot make ADH) → Fluid deprivation has dilute urine bc the pituitary can’t make ADH to retain water; desmopressin has concentrated urine because there is ADH to retain water

Urine Osm is unchanged after desmopressin and dilute after water deprivation

Nephrogenic DI (no response to ADH) → Dilute in fluid deprivation because there is no response to ADH, unchanged in desmopressin bc there is no response to ADH = no water retention

Growth hormone tests

GH suppression (glucose tolerance) test, insulin tolerance test, clonidine stimulation test

What is oral glucose tolerance in GH suppression

Find GH excess; Give 75g OGTT → Should suppress GH → If GH still high = secretion

What is insulin tolerance test

To diagnost GH def or AI; Give insulin → Hypoglycemic state → GH and Cortisol should rise to increase blood sugar → If low = def

How is insulin tolerance test done

Fast 8 hrs → Draw blood at 0,15,30,45,60,90,120 minutes → Test cortisol, GH and blood glucose

What is clonidine stimulation test

PEDIATRIC GH def; give clonidine (a2 adrenergic receptor) → GnRH release → Measure GH levels → if low = GH def