Updated: 3/11/2018

Hemolytic Uremic Syndrome (HUS)

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Snapshot
  • A 7-year-old boy recently had several episodes of bloody diarrhea. Desperate, his parents called his primary care physician, who reassured them that the infection is self-limited. Still concerned, his parents bought some diarrhea pills (anti-motility agents). A week later, he presents to the ER with jaundice, abdominal pain, and easy bruising. Lab results come back with low platelet count, anemia, and increased creatinine. A peripheral blood shows schistocytes. He is started on IV hydration.
Introduction
  • Syndrome commonly seen in children
    • most commonly caused by Escherichia coli O157:H7 (EHEC)  
      • acute diarrhea
      • due to Shiga-like toxin
    • S. pneumoniae infection
    • Shigella spp.
      • Shiga toxin
  • Classic triad
    • thrombocytopenia (first)
    • nonimmune microangiopathic hemolytic anemia (second)
    • acute renal failure (hence, “uremia” in title) (third)
  • Similar to TTP but without fever and neurologic symptoms
  • Pathogenesis
    • toxin damages endothelium
    • microthrombi form at site of damage
      • consumes platelets → thrombocytopenia
      • intravascular mechanical hemolysis → schistocytes
      • decreases renal blood flow → acute renal failure
  • Epidemiology
    • most commonly in children
    • exposed to E. coli
      • raw or undercooked meat
      • unwashed fruits/vegetables
      • animals at petting zoos
  • Risk factors
    • use of antimotility agents in EHEC diarrhea
    • use of antibiotics in EHEC diarrhea
Presentation
  • Symptoms
    • prodromal gastrointestinal illness
    • abdominal pain
    • bloody diarrhea
    • nausea
    • vomiting
    • fatigue (anemia)
    • oliguria/anuria (renal failure)
  • Physical exam
    • pallor (anemia)
    • jaundice (hemolysis)
    • petechiae/purpura uncommon
    • hepatosplenomegaly
Evaluation
  • Criteria for HUS
    • hemolytic anemia
      • hematocrit < 30%
      • schistocytes (helmet cells) on peripheral smear
    • thrombocytopenia 
    • ↑ serum creatinine
  • Normal PT/PTT
  • Negative Coombs test
  • ↑ bleeding time
Differential

 

Characteristics
DIC
ITP
TTP
HUS
Fever
  • No
  • No
  • Yes
  • Yes/No
Splenomegaly
  • No
  • No
  • Yes
  • Yes
Platelets
  • Low
  • Low
  • Low
  • Low
Bleeding time
PT
-
-
-
PTT
-
-
-
Shistocytes
  • Yes
  • No
  • Yes
  • Yes
Trauma
  • Yes
  • No
  • No
  • No

 

Treatment
  • Supportive care with fluids to maintain renal perfusion
    • dialysis if acute renal failure unresponsive to fluids
  • Fresh frozen plasma can be used (increases coagulation factor levels)
  • Plasmapheresis or plasma exchange for severe cases
Prognosis, Prevention, and Complications
  • Prognosis
    • 3-5% mortality
    • 5% severe sequelae such as end-stage renal failure
  • Prevention
    • prevent EHEC infection
      • avoid raw or undercooked meat
    • avoid antimotility agents or antibiotics
  • Complications
    • chronic kidney disease
    • hypertension
    • heart failure
    • electrolyte abnormalities
 

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(M2.HE.15.4673) A 6-year-old male presents to the emergency room complaining of severe abdominal pain. His mother notes that he has had several episodes of diarrhea for the past week, with vomiting over the past 3 days. The child is on summer vacation and attended a 4th of July barbecue 1 week ago. The patient's vital signs are as follows: T 38.3 C, HR 116, BP 110/75, SpO2 98%. Physical exam is remarkable for diffuse abdominal tenderness without rebound or guarding. CBC shows WBC 9 x10^3/uL, Hgb 10.2 g/dL, Hct 33%, Plt 46 x10^3/uL. Peripheral blood smear yields the following findings (Figure A). The patient's creatinine is found to be elevated at 1.3. What is the underlying cause of this patient's anemia? Tested Concept

QID: 107021
FIGURES:
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Chronic renal disorder

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Gastrointestinal arterio-venous malformation

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Poor dietary nutrition intake

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Inheritance of a beta-globin gene variant

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Toxin-mediated damage to endothelial cells and prothrombotic changes

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(M2.HE.15.33) A 6-year-old boy is admitted with a one-week history of diarrhea, which was sometimes bloody and originally began after a birthday party. He has become lethargic and has not been eating or drinking. His vital signs are as follows: T 38.5 C, HR 135, BP 82/54. Physical examination is significant for petechiae on his legs and diffuse abdominal tenderness to palpation. Lab-work shows BUN 72 mg/dL, creatinine 8.1 mg/dL, and platelet count < 10,000. PT and PTT are within normal limits. Which of the following would be expected on a peripheral blood smear? Tested Concept

QID: 104673
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Rouleaux formation

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Fragmented red blood cells

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Spur cells

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Giant platelets

3%

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No abnormalities

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