Value of degenerative change in neutrophils as a diagnostic test for Kawasaki syndrome

Study objective: To determine whether the presence of vacuoles and toxic granulation in neutrophils can be used as a diagnostic test to help differentiate children with Kawasaki syndrome from those with clinically similar illnesses. Design: Peripheral blood smears of 23 patients with Kawasaki syndrome, 23 disease control patients, and 23 hematology laboratory control subjects were examined in random order by technicians unaware of either the diagnosis or the previously recorded laboratory results. Setting: Tertiary care children's hospital in Ottawa, Canada. Patients: All 23 consecutive patients with Kawasaki syndrome satisfied established criteria for the diagnosis. Disease control patients were selected from the hospital registry of patients with other illnesses frequently considered as part of the differential diagnosis for Kawasaki syndrome. Measurements and main results: Compared with disease control patients, patients with Kawasaki syndrome had a higher percentage of neutrophils with vacuoles (mean±SEM, 31%±5% vs 14%±3%; p=0.006) and toxic granulation (mean±SEM, 43%±7% vs 14%±4%; p<0.001). If the sum of the number of neutrophils with vacuoles and the number with toxic granulation (per 100 maturen neutrophils examined) was at least 70, this "toxic neutrophil" test had a specificity of 0.96 and a likelihood ratio of a positive test result of 12. Conclusions: Degenerative change in noutrophils is common in the early stages of Kawasaki syndrome. The toxic neutrophil test is potentially a helpful adjunct to the clinical examination, particularly in the case of infants and other patients with subtle manifestations who might otherwise be at risk for delayed dlagnosis.