Differential Diagnosis

The patient's presentation of bloody diarrhea, fever, decreased urination, anemia, thrombocytopenia, schistocytes on the peripheral smear, and renal impairment suggests a complex condition involving the kidneys, blood, and possibly an infectious or immune-mediated cause. Here's a categorized differential diagnosis:

• Single most likely diagnosis

  • Hemolytic uremic syndrome (HUS): This condition is characterized by the triad of hemolytic anemia (indicated by anemia and schistocytes), thrombocytopenia, and acute kidney injury (suggested by decreased urination, elevated BUN, and creatinine). HUS is a common cause of acute kidney failure in children and is often preceded by a diarrheal illness, typically caused by E. coli O157:H7.

• Other Likely diagnoses

  • Henoch-Schonlein purpura (HSP): Although HSP can cause renal impairment and is associated with purpura, abdominal pain, and arthritis, the presence of schistocytes and the specific pattern of renal impairment and thrombocytopenia make it less likely than HUS in this case.
  • Salmonella enteritis: While Salmonella infections can cause bloody diarrhea and fever, they are less commonly associated with the full spectrum of HUS, including severe thrombocytopenia, schistocytosis, and significant renal dysfunction.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Thrombotic thrombocytopenic purpura (TTP): Although less common in children and not typically preceded by diarrhea, TTP can present with thrombocytopenia, microangiopathic hemolytic anemia, renal failure, and neurological symptoms. The distinction from HUS can be challenging and may require specific testing for ADAMTS13 activity.
  • Severe sepsis or meningitis: These conditions can cause multi-organ failure, including renal impairment and coagulopathy, and must be considered, especially if there are signs of severe infection or neurological involvement.

• Rare diagnoses

  • Immune thrombocytopenic purpura (ITP): ITP is characterized by isolated thrombocytopenia without other cytopenias or renal impairment, making it an unlikely diagnosis in this case.
  • Atypical HUS: This is a rare form of HUS not associated with diarrhea and is caused by complement pathway dysregulation. It could be considered if other causes of HUS are ruled out and there's a family history or recurrent episodes.
  • Other infections (e.g., Shigella, Campylobacter): While these can cause bloody diarrhea, they are less commonly associated with the full syndrome of HUS compared to E. coli O157:H7.