What are the laboratory findings of Kawasaki disease?

Laboratory Findings of Kawasaki Disease

The laboratory findings of Kawasaki disease (KD) include leukocytosis with neutrophil predominance, elevated inflammatory markers (ESR and CRP), thrombocytosis, anemia, hypoalbuminemia, elevated liver enzymes, and sterile pyuria, which collectively support diagnosis when clinical features are incomplete. 1

Key Laboratory Abnormalities

Hematologic Findings

• 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
• Leukopenia is rare and, when present, suggests an alternative diagnosis 1
• 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
• 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

Inflammatory Markers

• Elevation of acute phase reactants such as ESR and CRP is nearly universal in KD 1
• 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
• Finding of a minimally elevated ESR in the setting of severe clinical disease should prompt investigation for disseminated intravascular coagulation 1

Hepatic and Biochemical Abnormalities

• Mild to moderate elevations in serum transaminases or gamma-glutamyl transpeptidase occur in 40-60% of patients 1
• Mild hyperbilirubinemia occurs in approximately 10% of patients 1
• Hypoalbuminemia is common and associated with more severe and prolonged acute disease 1

Urinary Findings

• Urinalysis may show pyuria in up to 80% of children, although this finding lacks specificity for KD 1

Cerebrospinal Fluid Findings

• In children who undergo lumbar puncture, approximately 30% demonstrate pleocytosis with mononuclear cell predominance, normal glucose levels, and generally normal protein levels 1

Synovial Fluid Findings

• 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

Role in Incomplete Kawasaki Disease

• Laboratory tests provide support for a diagnosis of KD in patients with nonclassic but suggestive clinical features 1
• KD is unlikely if ESR, CRP, and platelet count are normal after day 7 of illness 1, 2
• The American Heart Association recommends additional laboratory testing for children with fever ≥5 days and 2-3 principal clinical features 1, 2
• 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 1

Evolution of Laboratory Values

• Laboratory values follow a consistent pattern of evolution before and after treatment 3
• White blood cell count, percentage bands, ESR, and CRP are highest in the acute phase before IVIG 3
• Platelet count peaks in the subacute phase (illness days 11-21) 3
• Percentage of lymphocytes and eosinophils are highest in the convalescent phase after IVIG 3

Diagnostic Pitfalls

• No single diagnostic test exists for KD; diagnosis remains clinical 2, 4
• Laboratory findings may be misinterpreted: sterile pyuria may be mistaken for partially treated urinary tract infection 1
• Cerebrospinal fluid pleocytosis may lead to misdiagnosis of viral meningitis 1
• Biomarkers currently under research have not yet demonstrated sufficient discriminative ability to replace standard laboratory tests 1, 4
• N-terminal pro-BNP may be elevated in some patients with KD but lacks clearly defined cut-point values 1

Laboratory Findings Associated with Outcomes

• Patients with coronary artery aneurysms tend to have higher white blood cell counts in the subacute phase and higher ESR in the subacute and convalescent phases 3
• Higher ESR, lower platelet count and hemoglobin levels are associated with IVIG resistance 5
• Hypoalbuminemia is associated with more severe and prolonged acute disease 1