Eosinophilia in children: characteristics, etiology and diagnostic algorithm

Eosinophilia is common in children and may be caused by various disorders. Large-cohort studies, including mild cases, are limited in children. This study aimed to reveal underlying etiologies of childhood eosinophilia and to create a diagnostic algorithm. Children (< 18 years) with absolute eosinophil counts (AECs) ≥ 0.5 × 10⁹/L were reviewed from medical files. Clinical characteristics and laboratory values were recorded. Patients were grouped based on the severity of eosinophilia as mild (0.5-1.5 × 10⁹/L), moderate (≥ 1.5 × 10⁹/L) and severe (≥ 5.0 × 10⁹/L). An algorithm was formed to evaluate these patients. We included 1178 children with mild (80.8%), moderate (17.8%) and severe eosinophilia (1.4%). The most common reasons of eosinophilia were allergic diseases (80%), primary immunodeficiency (PID) (8.5%), infectious diseases (5.8%), malignancies (0.8%) and rheumatic diseases (0.7%). Only 0.3% of children presented with idiopatic hypereosinophilic syndrome. Allergic diseases and PIDs were the most common etiologies in mild/moderate and severe groups, respectively. The median duration of eosinophilia was 7.0 (3.0-17.0) months in the study population and was the shortest in severe cases (2.0 (2.0-5.0) months). Multiple logistic regression analysis demonstrated food allergy [OR:1.866, 95%CI:1.225-2.842, p = 0.004] and PIDs [OR:2.200, 95%CI:1.213-3.992, p = 0.009] as independent factors for childhood eosinophilia. A diagnostic algorithm including mild form was presented for childhood eosinophilia.    Conclusion: Eosinophilia was frequently determined due to secondary causes; allergic diseases in mild/moderate eosinophilia, PIDs in severe group. Etiology of eosinophilia was diverse, and an algorithm concerning the severity of eosinophilia would be practical and rational. What is Known: • In children, eosinophilia is common, and mild eosinophilia occurs frequently. • Malignancies presents frequently with severe eosinophilia. What is New: • Primary immunodeficiencies were not a rare cause of eosinophilia, especially in countries such as the Middle East and eastern Mediterranean countries, where the countries consanguineous marriages are common, and should be investigated in children with eosinophilia who do not have allergic or infectious diseases. • In literature, there are many algorithms about childhood hypereosinophilia. However, mild eosinophilia is extremely important in children. Because all patients with malignancy and most of the patients with rheumatic diseases presented with mild eosinophilia. Therefore, we proposed an algorithm for childhood eosinophilia that includes mild eosinophilia besides moderate and severe cases.