PEDIATRIC HEMATOLOGY MCQS: ANSWER TO MCQ 05

MCQ: 05

CORRECT OPTION: 'B'

This patient presents with abdominal pain, fatigue, and decreased urination after a bloody diarrheal illness, which is concerning for hemolytic uremic syndrome (HUS). HUS most commonly occurs after infection with a Shiga toxin produced by a strain of Escherichia coli (01 57:H7). This toxin initially invades and destroys the colonic epithelial lining, producing bloody diarrhea and abdominal pain. Approximately 15% of children then develop the classic triad of HUS: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury (poor urine output, edema, and elevated creatinine and blood urea nitrogen).

The pathophysiology of HUS begins with systemic vascular endothelial injury and subsequent platelet microthrombi formation, which leads to thrombocytopenia and schistocytes as they flow through small vessels (including glomeruli). The resulting hemolytic anemia leads to decreased haptoglobin and elevated bilirubin causing scleral icterus and jaundice. Treatment is supportive (eg, fluid/electrolyte management, blood transfusions, dialysis).

(Choice A) Decreased ferritin levels are seen in patients with iron deficiency anemia. Patients with HUS would be expected to have normal or increased ferritin levels, as ferritin is an acute phase reactant that rises in the setting of inflammation.

(Choice C) Decreased reticulocyte counts in the setting of anemia are typically indicative of defective bone marrow (eg, viral suppression, aplastic anemia, malignancy). Reticulocyte counts are increased in the setting of hemolytic anemias.

(Choice D) Coagulation studies in HUS, including prothrombin time, are typically

normal. Thrombocytopenia and microangiopathic hemolytic anemia can be seen in both HUS a d disseminated intravascular coagulation (DIC), and abnormal coagulation studies can support the diagnosis of DIC.

(Choice E) The direct Coombs test is positive in patients with autoimmune hemolytic anemia. Because red blood cells are mechanically destroyed in HUS, the direct Coombs test will be negative.

Educational objective:

Hemolytic uremic syndrome, most commonly caused by Shiga toxin produced by Escherichia coli strain 0157:H7, is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.