A 6-year-old boy is brought to the office due to pallor and decreased energy. For the past 2 days, the patient has been less active, uninterested in playing, and sleeping throughout the day. On review of systems, the parents note that he developed a fever, emesis, and diarrhea 10 days ago, but his symptoms resolved without intervention after a few days. His older sister had a sore throat a few days ago, but no other family members have been ill. The patient has no chronic medical conditions. Temperature is 37.1 C (98.8 F), blood pressure is 120/70 mm Hg, and pulse is 145/min. Physical examination shows a tired-appearing boy with pale lips. A grade 2/6 systolic murmur is present. The lungs are clear to auscultation. The abdomen is soft, nontender, and nondistended. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 8.4 g/dL |
| Platelets | 30,000/mm3 |
| Leukocytes | 15,200/mm3 |
| Serum chemistry | |
| Blood urea nitrogen | 32 mg/dL |
| Creatinine | 2.4 mg/dL |
Which of the following is the most likely cause of kidney injury in this patient?
Show Explanatory Sources
This patient's prodromal diarrheal illness, followed by anemia (likely hemolytic), thrombocytopenia, and acute kidney injury (AKI), is consistent with hemolytic uremic syndrome (HUS). HUS is typically seen in children and usually occurs due to Shiga toxin–producing diarrheagenic pathogens such as Escherichia coli O157:H7 or, less commonly, Shigella. The production and systemic circulation of the Shiga toxin cause injury to small blood vessel endothelium, leading to a thrombotic microangiopathy and resultant:
renal vascular occlusion (eg, afferent arteriole, glomerular capillaries) by microthrombi; this blockage increases pressure within glomerular capillaries, leading to intrinsic acute kidney injury (eg, BUN/creatinine ratio of <20:1, oliguria, hypertension, hematuria, proteinuria).
platelet consumption within microthrombi, resulting in thrombocytopenia.
red blood cell (RBC) destruction due to physical RBC shearing from passage through blood vessels occluded by systemic microthrombi, resulting in a hemolytic anemia (eg, fatigue, pallor).
Treatment of HUS is supportive (eg, fluid management, transfusions) because most children (60%-70%) recover completely.
(Choice A) This patient's murmur and tachycardia could be indications of heart failure, possibly related to recent illness (eg, viral myocarditis, bacterial endocarditis), and decreased cardiac function can cause tubular injury from prolonged renal ischemia. However, this patient's acute anemia, thrombocytopenia, and AKI are most consistent with HUS, and his systolic flow murmur is likely due to severe anemia.
(Choice B) Although IgA vasculitis (Henoch-Schonlein purpura), a disease of the renal vasculature, can cause abdominal pain and AKI, patients typically have associated purpura (>75%) and joint pain (>80%); thrombocytopenia is unusual.
(Choice C) Poststreptococcal glomerulonephritis is a common cause of intrinsic renal injury in children but typically presents several weeks after group A streptococcal pharyngitis or impetigo with edema, hypertension, and hematuria. Anemia and thrombocytopenia are uncommon.
(Choice E) Acute renal vasoconstriction typically presents with prerenal AKI, which can occur in children who take nonsteroidal anti-inflammatory drugs during periods of hypovolemia (eg, gastroenteritis). However, patients typically have a normal complete blood count and a BUN/creatinine ratio of >20:1, making this diagnosis less likely.
Educational objective:
Hemolytic uremic syndrome (HUS) is characterized by the triad of hemolytic anemia, thrombocytopenia, and acute kidney injury (typically following a prodromal diarrheal illness caused by Escherichia coli O157:H7). The mechanism of intrinsic renal injury in HUS is renal vascular occlusion caused by capillary microthrombi.