Tests for the anterior pituitary function

Question 1

Basic hormones to be tested

Answer 1

LH, FSH, GH, Prolactin, ACTH, TSH

Question 2

Stimulation tests

Answer 2

Testing the hypothalamus, target gland stimulation tests, testing of the anterior pituitary with hypothalamic hormones (GnRH, GHRH, CRH, TRH)

Question 3

Tests used for hypothalamic function

Answer 3

Insulin hypoglycemia test
Clonidine/Arginine
Clomiphene
Metoclopramide

Question 4

Insulin hypoglycemia test

Answer 4

Induction of the stress response and thus release of ACTH, Prolactin and GH. Should not be used on patients older than 65, those with hypertension or with epilepsy

Question 5

Clonidine/arginine test

Answer 5

Stimulates the release of CRH

Question 6

Clomiphene test

Answer 6

Will test release of FSH and LH. It binds to the estrogen receptors for a prolonged period of time, and thus inhibit the secretion of estrogen. This will lead to a decreased negative feedback. and therefore an increase in FSH and LH

Question 7

Metoclopramide test

Answer 7

Leads to an increase in the secretion of Prolactin

Question 8

Tests used for target gland stimulation

Answer 8

Short synacten test, hCG test, Insulin tolerance test (ITT), glucose tolerance test, dexamethasone suppression test

Question 9

Short synacten test

Answer 9

It is a short ACTH stimulation test in order to assess the adrenal axis. Examine the plasma cortisol level before and 30 min after giving Tetracosactide (Synacten). Addisons disease is excluded if cortisol after 30 min is >550nmol/L

Question 10

hCG test

Answer 10

Tests for LH and FSH

Question 11

Insulin tolerance test (ITT)

Answer 11

Used to assess adrenal and GH axes. It tests for cortisol release from the adrenals and if there is damage to the pituitary which will cause GH decrease. Contraindicated in patients with epilepsy, heart disease, adrenal failure.
Done in the morning by injecting IV insulin to induce hypoglycemia, which causes a stress response and thus ACTH and GH secretion. Glucose must fall below 2.2 mM. Normal is when GH >20mU/L and peak cortisol >550nmol/L. When ITT is contraindicated, use arginine + GHRH test; a glucagon stimulating test

Question 12

Glucose tolerance test (OGTT)

Answer 12

Along with GH measurements. It is preformed if acromegaly is suspected. The test is done at 09:00 in the morning after a night of fasting. GH and glucose samples are taken at 0,30,60,90,120,150 min. Normally the GH levels should be inhibited by an increase in glucose, however in acromegaly this is not the case.
False positive tests can occur in puberty, pregnancy, hepatic and renal disease, anorexia nervosa, and DM)

Question 13

Dexamethasone test

Answer 13

Screening test to diagnose and differentiate among types of Cushings and other hypercortisol states. Give dexamethasone 1mg at midnight. Check the serum cortisol before, and at 8AM the next morning.
In normal patients the large increase in steroids cause negative feedback on ACTH and thus cortisol secretion is reduced to <50 nmol/L. In Cushings syndrome there is failure to suppress the cortisol secretion