How is the diagnosis of Adrenal Insufficiency made?

First the biochemical diagnosis must be made. The adrenal cortical hormone levels must be shown to be lowered.

  • Basal Cortisol Secretion
    A low plasma cortisol level (<140nmol/L) in these situations is evidence of adrenal insufficiency. Plasma cortisol levels are normally high in the early morning and increase with stress.

    • Circadian rhythm of cortisol

    Circadian rhythm of cortisol - click to enlarge

  • Response to Acute ACTH Stimulation
    An impaired response in a low dose ACTH stimulation test (Synacthen Test), using an ACTH analogue, Tetracosactrin confirms adrenal insufficiency. A normal response is a rise in plasma cortisol levels after 30-60 minutes.

Distinguishing between primary, secondary and tertiary adrenal insufficiency.

In primary adrenal insufficiency, basal early morning plasma ACTH concentrations are elevated compared to the low normal levels found in secondary and tertiary disease.

Primary adrenal insufficiency can also be distinguished from secondary and tertiary by using a prolonged ACTH stimulation test. Stimulation of the adrenal gland in primary disease will not result in the release of cortisol. In secondary and tertiary insufficiency the atrophic adrenal glands still produce some cortisol when exposed to ACTH.

Secondary can be distinguished from tertiary adrenal insufficiency by monitoring the ACTH response to stimulation with CRH. There is little or no ACTH response in patients with secondary adrenal insufficiency, but there is a significant ACTH response in patients with tertiary adrenal insufficiency.

The cause of this insufficiency must then be elucidated. This is done by considering the following:

  • The patient's age (certain causes are more prevalent at certain ages)
  • Other autoimmune disorders (indicates increased probability of an autoimmune cause)
  • Abdominal CT scan (enlarged or calcified adrenals eliminates autoimmune disease)
  • Patients presenting with tuberculous adrenal insufficiency usually have TB elsewhere
  • A pituitary CT or MRI scan should be performed to exclude a tumour as the cause of secondary or tertiary adrenal insufficiency
  • Drug induced