What are the laboratory findings and diagnostic criteria for Kawasaki disease?

Kawasaki Disease: Laboratory Findings and Diagnostic Criteria

Kawasaki disease is diagnosed primarily based on clinical criteria, including fever for at least 5 days plus 4 out of 5 principal clinical features, with laboratory tests serving as supportive evidence when the clinical presentation is incomplete or atypical. 1

Principal Clinical Diagnostic Criteria

• Fever persisting at least 5 days (typically >102.2°F/39°C, often >104°F/40°C) 1, 2
• Plus at least 4 of the following 5 principal features:
  • Changes in extremities: Acute erythema and edema of hands and feet, followed by periungual desquamation in the convalescent phase 1, 2
  • Polymorphous exanthema (rash) 1, 2
  • Bilateral, painless bulbar conjunctival injection without exudate 1, 2
  • Changes in lips and oral cavity: Erythema and cracking of lips, strawberry tongue, diffuse injection of oral and pharyngeal mucosae 1, 2
  • Cervical lymphadenopathy (≥1.5 cm in diameter), usually unilateral 1, 2

Laboratory Findings

When evaluating a child with suspected Kawasaki disease, the following laboratory abnormalities are commonly observed:

• Inflammatory markers:

  • Elevated erythrocyte sedimentation rate (ESR) 3, 2
  • Elevated C-reactive protein (CRP) 3, 2
  • Elevated serum ferritin levels may be present 4

• Complete blood count:

  • Leukocytosis with neutrophil predominance 3, 2
  • Thrombocytosis (typically appears after 7-10 days of illness) 3, 2
  • Normocytic, normochromic anemia 2

• Urinalysis:

  • Sterile pyuria (white blood cells in urine without infection) 3, 2

• Liver function tests:

  • Elevated serum transaminases 1, 2
  • Hypoalbuminemia 1, 2

• Other findings:

  • Elevated serum lipids 2
  • Hyponatremia 2
  • Cerebrospinal fluid: pleocytosis (in cases with meningeal involvement) 2

Diagnostic Approach for Incomplete Kawasaki Disease

For children with fever ≥5 days and only 2-3 principal clinical features, the American Heart Association recommends: 3, 2

1. Check inflammatory markers (CRP ≥3.0 mg/dL and ESR ≥40 mm/hr) 3
2. If inflammatory markers are elevated, assess for supplemental laboratory criteria:
   • Albumin ≤3.0 g/dL
   • Anemia for age
   • Elevation of alanine aminotransferase
   • Platelets after 7 days ≥450,000/mm³
   • White blood cell count ≥15,000/mm³
   • Urine ≥10 white blood cells/high-power field
3. If ≥3 supplemental laboratory criteria are present, treat for Kawasaki disease 3
4. Obtain echocardiogram if laboratory criteria are met 3

Special Diagnostic Considerations

• Diagnosis can be made with fewer than 5 days of fever if typical clinical findings are present 1, 3
• Classic Kawasaki disease can be diagnosed with only 3 clinical features if coronary artery abnormalities are detected on echocardiography 1, 3
• Infants <6 months may present with only prolonged fever and irritability, yet have a high risk of coronary abnormalities 3
• Older children and adolescents often have delayed diagnosis and higher prevalence of coronary artery abnormalities 3

Common Pitfalls in Diagnosis

• Clinical features may not all be present simultaneously; careful history-taking is essential 1, 2
• Incomplete (atypical) Kawasaki disease should be considered in any child with unexplained persistent fever 3, 2
• Kawasaki disease must be differentiated from other conditions with similar presentations, including viral infections (measles, adenovirus) and bacterial infections (scarlet fever, staphylococcal scalded skin syndrome) 3, 2
• No specific diagnostic test exists for Kawasaki disease; diagnosis remains clinical 1, 3

Early diagnosis and treatment with IVIG and aspirin within 10 days of fever onset significantly reduces the risk of coronary artery abnormalities, which develop in 15-25% of untreated children 3, 2, 5.