LabMed

Low Serum Cortisol

Differential Diagnosis

Primary adrenal insufficiency

Secondary adrenal insufficiency with underlying disorder

Suggested Additional Lab Testing

Primary adrenal insufficiency

  • Exogenous ACTH does not stimulate cortisol secretion, and the plasma ACTH is elevated.

  • Serum aldosterone is low in cases in which destruction of the adrenal gland affects both cortisol and aldosterone production.

  • Testing for antibodies against the adrenal cortex may reveal autoimmune adrenalitis as a cause of primary adrenal insufficiency.

Secondary adrenal insufficiency

  • Low plasma ACTH, because the disorder originates in the hypothalamus or pituitary.

  • Serum aldosterone is often normal but may be decreased if there is significant atrophy of the adrenal gland as a result of chronic lack of stimulation by ACTH.

  • CRH stimulation test can distinguish between ACTH deficiency from pituitary and deficiency of CRH from hypothalamus.

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