Typical Presentation of Hemolytic Uremic Syndrome in Children
Children with HUS classically present with bloody diarrhea that develops 1-5 days after initial non-bloody diarrhea, followed 4-5 days later by the diagnostic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. 1
Prodromal Phase (Days 1-7)
The illness begins with an acute gastrointestinal infection:
- Non-bloody diarrhea appears first, typically after consuming contaminated ground beef, unpasteurized milk/juice, or raw produce 1
- Progression to bloody diarrhea occurs in approximately 60-80% of cases within 1-5 days after diarrhea onset 1, 2
- Abdominal pain or tenderness is prominent, often considerable in severity 2, 3
- Five or more stools in 24 hours before presentation is characteristic 2
- Pain on defecation is common 2
- Absence of fever at time of presentation is a distinguishing clinical clue 2
HUS Phase (Days 4-12 after diarrhea onset)
The classic triad develops approximately 4-5 days after diarrhea begins 1:
Microangiopathic Hemolytic Anemia
- Pallor and fatigue from acute-onset anemia 1
- Elevated LDH, reduced haptoglobin, and elevated indirect bilirubin as hemolysis markers 1, 4
- Schistocytes, burr cells, or helmet cells on peripheral blood smear 4, 5
- Negative direct Coombs test confirming non-immune hemolysis 4, 5
Thrombocytopenia
- Platelet count <150,000/mm³ detected early in illness 1, 5
- Often asymptomatic but may present with petechiae or bruising 6
Acute Kidney Injury
- Oliguria or anuria develops as renal failure progresses 7, 6
- Hematuria and proteinuria on urinalysis 4, 5
- Elevated serum creatinine (≥1.0 mg/dL in children <13 years) 4, 5
- Hypertension and volume overload from fluid retention 1
Age-Specific Considerations
- Children under 5 years have the highest incidence and represent the primary demographic for typical HUS 1
- HUS is the most common cause of acute renal failure requiring dialysis in young children 1, 3, 7
Severe Complications (10-20% of cases)
- Neurological involvement including seizures, altered mental status, or stroke is the first cause of death 1
- Intussusception can occur as a gastrointestinal complication 3
- Chronic renal failure develops in a subset of patients due to nephron loss 7
Critical Diagnostic Timing
The timing sequence is diagnostically crucial: diarrhea precedes HUS by 4-5 days in typical STEC-HUS, whereas simultaneous onset of diarrhea and HUS suggests atypical HUS requiring different management 1, 5. This approximately one-week incubation period between diarrhea onset and HUS development requires physicians to maintain high clinical suspicion and perform early laboratory testing 3.
Key Clinical Pitfalls
- Near-normal hemoglobin may indicate dehydration masking anemia rather than absence of disease 1
- Not all three components of the triad may be clearly present at disease onset in up to 50% of cases 5
- Absence of schistocytes should not exclude early diagnosis due to low sensitivity 1, 5
- Antibiotic use during the diarrheal phase may worsen outcomes and increase HUS risk 1