What is the role of lab testing in the workup of hypopituitarism (panhypopituitarism)?

Updated: Jun 09, 2020
  • Author: Bernard Corenblum, MD, FRCPC; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

Hormonal studies should be performed in pairs of target glands and their respective stimulatory pituitary hormone for proper interpretation, as follows [4] :

  • ACTH (Cortrosyn) stimulation test (or morning cortisol and ACTH); may need hypoglycemia or glucagon stimulation testing

  • TSH and thyroxine

  • FSH, LH, and either estradiol (if amenorrheic) or morning testosterone (as appropriate for sex)

  • Prolactin

  • GH provocative testing with various stimulation tests

Corticotropin deficiency may be evident with the finding of a decreased serum cortisol level. However, a low cortisol level may not help to distinguish primary adrenal insufficiency from secondary adrenal insufficiency due to hypopituitarism. The conditions can be differentiated on clinical grounds. A patient with secondary causes due to pituitary dysfunction has a relatively pale complexion (not hyperpigmented), a normal aldosterone response, normal serum potassium, and low/normal morning ACTH level, measured in the morning due to its highest circadian levels. Hyponatremia may occur.

The opposite is true for primary adrenal insufficiency. Hyperpigmentation in primary adrenal insufficiency is due to increased ACTH production with concomitant overproduction of melanocyte-stimulating hormone, which is coupled with ACTH in a mutual precursor. ACTH elevation, measured any time, suggests an adrenal etiology. Hyperkalemia may be present, owing to concomitant aldosterone deficiency, which does not occur with ACTH insufficiency. Hyponatremia may result from cortisol insufficiency, and thus does not separate pituitary from adrenal disease.


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