Hemolytic uremic syndrome (HUS) is an acute syndrome defined by a triad of hemolytic anemia, thrombocytopenia, and acute renal failure. The condition occurs in both children and adults, although it is more common in children and is among the leading causes of acute renal failure in the pediatric population. The etiology of HUS is not fully understood. HUS presents in 2 ways, either as an idiopathic condition or in response to a stressor. Shiga toxin-producing Escherichia coli (often E coli O157:H7 strain) is a leading cause of HUS, although Streptococcus pneumonia and human immunodeficiency virus (HIV) infection can also cause HUS.

Shiga toxin damages the renal epithelial cells, mesangial cells, and vascular endothelial cells. Drug toxicity, pregnancy, antiphospholipid antibody syndrome, and systemic lupus erythematosus have also been reported to induce HUS. Cases of HUS not associated with an acute stressor are thought to be caused by complement pathway dysregulation. Gene mutations (C3, C4BPA, C4BPB, MCP, CFB, CFH, CFHR1, CFHR3, CFHR4, CFHR5, CFI, DGKE, and THBD) are identified in approximately 70% of nonstressor-induced HUS.

HUS is a rare condition. In children younger than 5 years of age in the United States and Western Europe, the incidence of Shiga toxin-producing HUS is approximately 2-3 per 100 000 children. Escherichia coli O157:H7 is estimated to account for 90% of these cases. HUS without an identifiable trigger is less common, with an estimated incidence of 7 per one million in this population.

HUS triggered by an infection presents with hematochezia, fever, abdominal pain, nausea, and emesis. Clinical findings related to acute renal failure can include anuria or oliguria, hypertension, elevated creatinine, elevated blood urea nitrogen (BUN), proteinuria, microscopic hematuria, and pyuria. Idiopathic HUS will present without concurrent infectious symptoms. Hemolytic anemia, thrombocytopenia, and acute renal failure can present insidiously with lethargy and uremia, or patients may present with a petechial rash, scattered ecchymosis, or hematuria. In these cases, a family history of HUS can help inform consideration of the diagnosis, as many of the complement pathway mutations are inherited.

Treatment is dependent on severity and is mainly supportive, including fluid replacement, blood product transfusions, avoidance of nephrotoxic medications, and dialysis. HUS can progress to end-stage renal disease requiring renal replacement therapy and ultimately renal transplant. However, prognosis is generally good, especially in children. An estimated 25% of children will have acute renal injury, while approximately 3% develop end-stage renal disease requiring hemodialysis with potential renal transplantation. Pneumococcal-associated HUS has a higher mortality, estimated to be around 12%, with approximately 10% developing end-stage renal disease.