Low platelet count, immunoglobulin resistance, and coronary artery involvement in Kawasaki disease

Lower platelet count is associated with intravenous immunoglobulin (IVIG) resistance in Kawasaki disease (KD); paradoxically, higher count is associated with coronary artery (CA) sequelae. We addressed this inconsistency.

Using a large-scale nationwide KD database in Japan, we standardized platelet counts by age and hospital visit day. We evaluated associations between standardized platelet count and IVIG resistance using multivariable modified Poisson regression models. Associations between platelet count and CA sequelae were assessed separately among IVIG-resistant and IVIG-responsive patients.

In 41,540 patients, lower standardized platelet counts were associated with IVIG resistance in all age groups and the association increased with age: adjusted risk ratios with 95% confidence intervals per standardized platelet count decrease of 1 were 1.15 [1.06-1.25] at 0-5 months, 1.08 [1.02-1.15] at 6-11 months, 1.18 [1.14-1.22] at 1-2 years, 1.22 [1.17-1.27] at 3-4 years, and 1.26 [1.19-1.33] at ≥5 years. Lower standardized platelet count was also associated with CA sequelae in IVIG-resistant patients (1.12 [1.02-1.23]), but not in IVIG-responsive patients (0.95 [0.86-1.04]).

Lower platelet counts were associated with IVIG resistance and CA sequelae in IVIG-resistant patients. Early platelet evaluation may identify high-risk patients with KD.

Previous studies of platelet counts have shown conflicting results: lower platelet counts were associated with immunoglobulin resistance, but higher platelet counts were associated with coronary artery complications. Lower platelet counts were associated with immunoglobulin resistance across all age groups. Moreover, lower platelet counts were associated with coronary artery complications, but this association was found only in immunoglobulin-resistant patients. Our study resolves previous conflicting results by properly adjusting for age, immunoglobulin responsiveness, and platelet examination timing. Early platelet count evaluation may aid in identifying patients at high risk of immunoglobulin treatment failure and subsequent coronary involvement.