Thread by @WilliamAird4

1/7

NAME THAT CBC

I tweeted a pair of CBCs earlier today and asked for a diagnosis in two words.

Lots of great responses!!

Kudos to @AaronBoothby2 for getting the right answer:

CLOSTRIDIAL SEPSIS

In this thread we will systematically work through the case.

2/7

1. The first thing to note is that the two CBCs were taken a mere 7 h apart. Many notable changes occurred during this short time span, including a sudden drop in Hb and MCV and an increase in MCHC and RDW.

... it is the CHANGES in values that are meaningful.

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2. How can we explain such a rapid drop in Hb? Certainly not by a production problem. If I completely shut off my bone marrow production of RBCs, my Hb will only drop by 0.1 g/dL/day because of the long survival time of RBCs.

So, this must be hemolysis or hemodilution.

4/7

3. Let's consider hemodilution first (which would most likely occur in the context of a bleed). If we work through the numbers we find that the patient would have had to receive a ridiculous quantity of fluid to explain this degree of drop in Hb.

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4. That leaves hemolysis as the most likely cause of the reduction in Hb. The ddx of hemolysis includes immune and non-immune causes (extracorpuscular and intracorpuscular).

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5. Considering causes of HA that are associated with elevated MCHC, the ddx narrows to AIHA (real), CAD (artifact) and infection with clostridial perfringens (real).

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6. The MCV in CAD is artificially elevated, whereas this patient's MCV actually decreased (albeit within the normal range). The latter result is c/w AIHA or clostridium sepsis (especially the latter owing to microspherocytes).

7/7

7. It would very unusual for a warm antibody to result in such rapid hemolysis. Moreover, the leukocytosis is a hint that there may be an underlying infection.

In fact this patient had fulminant clostridial sepsis (including classical microspherocytes on his blood smear).