Laboratory Findings of Kawasaki Disease
Key Laboratory Abnormalities
- The American Heart Association notes that leukocytosis is typical during the acute stage, with predominance of immature and mature granulocytes; approximately 50% of patients have white blood cell counts >15,000/mm³ 1, 3
- Leukopenia is rare and, when present, suggests an alternative diagnosis 1, 2
- Anemia (normochromic and normocytic) is common and resolves with resolution of inflammation 1
- Thrombocytosis is characteristic but generally does not occur until the second week of illness, peaking in the third week (mean ≈700,000/mm³) and normalizing by 4-6 weeks 1, 2
- Thrombocytopenia is rare but may occur in the first 1-2 weeks and can be a sign of disseminated intravascular coagulation; it's a risk factor for coronary artery abnormalities 1, 4
- Elevation of acute phase reactants such as ESR and CRP is nearly universal in KD 1, 3
- CRP normalizes more quickly than ESR during resolution of inflammation 1
- ESR is elevated by IVIG therapy, making it less useful for monitoring response to treatment 1, 2
- Finding of a minimally elevated ESR in the setting of severe clinical disease should prompt investigation for disseminated intravascular coagulation 1
- Mild to moderate elevations in serum transaminases or gamma-glutamyl transpeptidase occur in 40-60% of patients 1, 2
- Mild hyperbilirubinemia occurs in approximately 10% of patients 1
- Hypoalbuminemia is common and associated with more severe and prolonged acute disease 1, 2
- Urinalysis may show pyuria in up to 80% of children, although this finding lacks specificity for KD 1, 4
- In children who undergo lumbar puncture, approximately 30% demonstrate pleocytosis with mononuclear cell predominance, normal glucose levels, and generally normal protein levels 1, 2
- In patients with arthritis, arthrocentesis typically yields purulent-appearing fluid with a white blood cell count of 125,000-300,000/mm³, normal glucose level, and negative Gram stain and cultures 1
Laboratory Findings in Diagnosis
- Laboratory tests provide support for a diagnosis of KD in patients with nonclassic but suggestive clinical features 1, 5
- KD is unlikely if ESR, CRP, and platelet count are normal after day 7 of illness 1, 6
- The American Heart Association recommends additional laboratory testing for children with fever ≥5 days and 2-3 principal clinical features 6, 7
- Supplemental laboratory criteria include: anemia for age, platelet count ≥450,000/mm³ after the 7th day of fever, albumin <3.0 g/dL, elevated ALT level, WBC count ≥15,000/mm³, and urine ≥10 WBC/hpf 7
Diagnostic Pitfalls
- No single diagnostic test exists for KD; diagnosis remains clinical 6
- Laboratory findings may be misinterpreted: sterile pyuria may be mistaken for partially treated urinary tract infection 3, 5
- Cerebrospinal fluid pleocytosis may lead to misdiagnosis of viral meningitis 7
- Biomarkers currently under research have not yet demonstrated sufficient discriminative ability to replace standard laboratory tests 1
- N-terminal pro-BNP may be elevated in some patients with KD but lacks clearly defined cut-point values 1, 4