The 2-week time interval criterion may alter the spectrum of disease and patient characteristics in children diagnosed with hypereosinophilia

<b>Background.</b> Diagnostic criteria for hypereosinophilia (HE) have been revised. Accordingly, the minimum interval between the two results with an absolute eosinophil count (AEC) ≥ 1500 cells/µL has been reduced from 4 to 2 weeks. The aims of this study were to identify patients with HE according to the new diagnostic criteria in children and demonstrate the effects of the revised time interval criterion on patient characteristics and disease spectrum. <b>Methods.</b> Individuals aged ≤ 18 years admitted to a tertiary university hospital were identified using an algorithm based on old and new diagnostic criteria for HE. While patients diagnosed with HE according to old diagnostic criteria were included in group 1, patients who were diagnosed with HE according to the new diagnostic criteria but did not meet the old criteria were included in group 2. <b>Results.</b> Patients in group 1 were significantly older than patients in group 2 at the time of diagnosis of HE (p = 0.004). While the number of patients diagnosed with HE aged 1-5 years was higher in group 1 (p = 0.01), the number of patients diagnosed with HE under the age of one year was higher in group 2 (p = 0.002). The most common cause of HE in group 1 was allergic disorders (10/40, 25%), while non-parasitic infections (17/36, 47%) were the most common diagnosis in group 2. <b>Conclusions.</b> The new diagnostic criteria may change the characteristics of pediatric patients with HE and the spectrum of associated diseases.