Case puzzler:  A patient was admitted to ICU due to profound hypotension of unknown cause.  What *two* clues are contained in the CBC which reveal the diagnosis?

Answer

In isolation, this data wouldn't be very exciting.  However, there are two things which are strange about this CBC in the context of a shocked patient.

Clue #1:  Eosinophilia.

Normally, shocked patients produce lots of cortisol.  Cortisol suppresses the eosinophil count.  Therefore, it's common to see patients with severe shock have reduced numbers of eosinophils (frequently zero).  The presence of an elevated absolute eosinophil count in a shocked patient should immediately suggest adrenal insufficiency.  More on this in the IBCC chapter on adrenal insufficiency here.

Clue #2:  Normal neutrophil/lymphocyte ratio (NLR)

The neutrophil to lymphocyte ratio (NLR) is a marker of physiologic stress.  In a shocked patient, this really ought to be elevated.  However, this patient's NLR is 33/22 = 1.8/1.2 = 1.5 (you can calculate the NLR using either absolute or relative cell counts).  A NLR on the low end of normal is really strange in a patient with shock.

One of the major drivers of NLR is the cortisol level (cortisol increases the neutrophil count and reduces the lymphocyte count):

Stress ==> Cortisol ==> Elevated NLR

So the presence of clinical shock with a normal NLR suggests an inadequate cortisol level (i.e. adrenal insufficiency).

This might be the first case report of an inappropriately normal NLR being used to diagnose adrenal crisis.  So I can't comment on the sensitivity or specificity of a normal NLR to diagnose adrenal insufficiency.  More on the NLR here.

Case resolution:  The patient was started immediately on IV dexamethasone 6 mg with clinical improvement.  Meanwhile an ACTH stimulation test was performed which confirmed the presence of adrenal insufficiency.

A similar case:  This may not be quite as much of a zebra as it might seem.  After posting this to twitter. Dr. Ghent related a similar case:

Similar case recently. To ED with low pressures but well-appearing, NLR 2.6. DC after fluids. Next day shock, thought to be septic, NLR 1.4. No eosinophilia. Arrest. ECMO. Final dx: empty sella 2/2 Sheehan's causing secondary adrenal insufficiency. Walked out neuro intact.

— Garrett Ghent (@GarrettGhentMD) September 16, 2019