Does a patient with Kawasaki disease typically have thrombocytopenia (low platelet count)?

Platelet Count in Kawasaki Disease

No, Kawasaki disease does not typically present with low platelets—thrombocytosis (elevated platelet count) is the characteristic finding, usually appearing in the second to third week of illness with mean counts around 700,000/mm³. 1

Typical Platelet Pattern in Kawasaki Disease

Thrombocytosis is the hallmark platelet abnormality in Kawasaki disease, not thrombocytopenia. 1 The characteristic pattern includes:

• Platelet counts generally remain normal or low-normal during the first week of illness 1
• Thrombocytosis typically does not occur until the second week of illness, peaking in the third week 1
• Mean peak platelet counts reach approximately 700,000/mm³ 1
• Platelet counts normalize by 4-6 weeks after illness onset 1
• During acute and subacute phases, platelets increase in number AND become activated, contributing to thrombotic risk 2

Thrombocytopenia: A Rare but Serious Finding

While uncommon, thrombocytopenia (low platelets) can occur in Kawasaki disease and represents a significant warning sign:

• Thrombocytopenia is rare but may occur in the first 1-2 weeks of illness 1
• When present, thrombocytopenia is a risk factor for coronary artery abnormalities 1
• Thrombocytopenia can be a sign of disseminated intravascular coagulation (DIC) 1
• Patients with thrombocytopenia have significantly higher rates of coronary artery aneurysms (60% vs 8.9% in controls) and acute myocardial infarction (40% vs 0.3% in controls) 3

Mechanism of Thrombocytopenia When Present

In most cases where thrombocytopenia occurs, it results from intravascular coagulation rather than decreased production: 3

• Low fibrinogen concentrations, high fibrin degradation products, and discordant inflammatory markers (low ESR with high CRP) suggest consumptive coagulopathy 3
• Less commonly, bone marrow examination may show immature megakaryocytes with normal coagulation studies 3
• The inflammatory insult of Kawasaki disease on bone marrow may affect various cell lineages 4

Clinical Implications and Diagnostic Pitfalls

A minimally elevated ESR in the setting of severe clinical disease should prompt investigation for DIC, which may present with thrombocytopenia. 1

Key Diagnostic Points:

• After day 7 of illness, Kawasaki disease is unlikely if ESR, CRP, AND platelet count are all normal 1
• Platelet count ≥450,000/mm³ after the 7th day of fever is one of the supplemental laboratory criteria supporting diagnosis of incomplete Kawasaki disease 1
• Thrombocytopenia at presentation should raise suspicion for severe disease and prompt aggressive monitoring for cardiac complications 3

Treatment Considerations:

For patients with rapidly expanding coronary artery aneurysms or maximum Z score ≥10, systemic anticoagulation with LMWH or warfarin plus low-dose aspirin is reasonable, particularly given the activated platelet state. 2

Immune-mediated cytopenias including autoimmune hemolytic anemia and immune thrombocytopenia are rarely seen at presentation but have been reported, requiring high clinical suspicion even in absence of typical laboratory findings. 5