A 5-year-old boy is brought to the emergency department due to 2 days of dark, low-volume urine and decreased energy. The parents say that the boy had abdominal pain, fever, and bloody diarrhea for 4 days, which resolved about 3 days ago without treatment. The day before the onset of symptoms, the patient swam in a lake and ate hamburgers at a family picnic. His vital signs are within normal limits. Physical examination shows pallor but is otherwise normal. He has no peripheral edema or rashes. Laboratory evaluation shows anemia, thrombocytopenia, and elevated blood urea nitrogen and serum creatinine. Which of the following findings is most likely to be seen in this patient?
Hemolytic uremic syndrome | |
Etiology | Shiga toxin–producing bacteria
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Clinical features |
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This patient has hemolytic uremic syndrome (HUS), which is most often caused by infection with shiga toxin-producing organisms such as Escherichia coli O157:H7 or Shigella dysenteriae. Shiga toxin (verotoxin) enters the circulation from the bowel and induces capillary endothelial damage, resulting in platelet activation with the formation of microthrombi. Platelet consumption causes thrombocytopenia whereas the microthrombi lead to erythrocyte damage (forming schistocytes) and the resultant hemolytic anemia (eg, pallor, weakness, tachycardia). Damage to glomerular endothelial cells also causes acute kidney injury (eg, oliguria/anuria, increased creatinine) in approximately 50% of cases.
The hemolytic anemia in HUS causes decreased hemoglobin and haptoglobin levels as well as increased serum lactate dehydrogenase and unconjugated bilirubin levels (Choice A). The bleeding time may also be increased due to the reduced number of platelets. However, other coagulation studies are normal as there are no clotting factor deficiencies or disseminated intravascular coagulation associated with HUS (Choices C and D).
(Choice E) Coombs test, or direct antiglobulin test, detects autoantibodies against red blood cells if they are present in the serum. The hemolytic anemia of HUS syndrome is mechanical rather than autoimmune; therefore, the Coombs test is negative.
(Choice F) Streptozyme testing detects antibodies against group A Streptococcus and can be used to retrospectively diagnose streptococcal infections (eg, when evaluating for post-streptococcal glomerulonephritis [PSGN]). However, children with PSGN have edema and hypertension, but no hemolytic anemia.
Educational objective:
Hemolytic uremic syndrome (HUS) manifests with acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. Characteristic laboratory abnormalities include decreased hemoglobin and platelet count and increased bleeding time, lactate dehydrogenase, bilirubin, blood urea nitrogen, and creatinine.