Day #25 - Adrenal Insufficiency

Today we talked about a case of a woman with a history of chronic steroid use who presented with refractory hypotension and hypoglycemia in the context of a systemic infection. The team were highly suspicious that this represented adrenal insufficiency in the context of a stressor. I wanted to touch upon how one can make the laboratory diagnosis of adrenal insufficiency.

The first step is to obtain morning (8AM) measurements of cortisol and ACTH.

• If the cotisol is below 80nmol/L the diagnosis is confirmed. If the ACTH is high, this suggests primary adrenal insufficiency, if the ACTH is inadequate this suggests secondary or tertiary adrenal insufficiency
  
• If the cortisol is above 500nmol/L the diagnosis is essentially excluded.
• If the cortisol is between 80-500, dynamic testing is required

The downside is that ACTH takes a long time to come back, and often you don't want to wait until 8am to make the diagnosis.

Dynamic testing (can happen at any time of day when the lab is open):
Obtain baseline cortisol measurement.
Then administer cosyntropin 250mcg IV
Then obtain cortisol measurements at 30 and 60 minutes post injection

If the cortisol increases to >550nmol/L then primary adrenal insufficiency is excluded and probably secondary as well -- although not definitively. If you have a high index of suspicion for secondary or tertiary adrenal insufficiency you should probably consult an endocrinologist as you will need specialized testing (i.e. CRH stimulation test, insulin induced hypogylcemia test, metrapyrone test)

In suspected adrenal crisis, you should obtain a STAT cortisol and ACTH measurement then start treatment with steroids and IV saline. Dexamethasone is preferable because it won't be picked up on the cortisol assay and consequently you can continue treatment while working up the patient. Remember that dexamethasone can suppress ACTH release, and so you will need to do dynamic testing unless the baseline studies are diagnostic.