Question

Diarrhea-related hemolytic uremic syndrome is characterized by all of the following, EXCEPT

• A. Acute renal failure
• B. Coombs' positive hemolytic anemia
• C. Thrombocytopenia
• D. Neutrophilic leukocytosis

Hint:

Ask whether the red cell breakdown in HUS is antibody driven or purely mechanical.

Answer 1

The Correct Option is B

This question checks the classic triad of hemolytic uremic syndrome (HUS), the illness that often follows a diarrheal infection caused by Shiga toxin producing bacteria. Let's go through each option one by one.

1. Acute renal failure: This is one of the three core features of HUS. Tiny clots form in the small vessels of the glomeruli and choke off blood flow to the kidney.
2. Coombs' positive hemolytic anemia: This one does not belong. HUS destroys red cells by physically shredding them as they squeeze past vessels packed with platelet clots, so the Coombs test, which picks up antibody sitting on the red cell, stays negative.
3. Thrombocytopenia: Platelets get consumed while building the small clots inside injured vessels, so a low platelet count is expected and forms part of the triad.
4. Neutrophilic leukocytosis: A rise in neutrophil count is a common lab finding seen during the acute stage of the disease.

Three of the four options are genuine features of HUS, so the odd one out is the Coombs positive finding, because the hemolysis in HUS is mechanical and not antibody driven.

Let's summarize:

• HUS shows a triad of hemolytic anemia, thrombocytopenia, and acute renal failure.
• The hemolysis is microangiopathic and Coombs negative, never Coombs positive.

So the finding that does not belong with HUS is Coombs' positive hemolytic anemia.