To the Editor, Blood hypereosinophilia (HE), defined as eosinophils in peripheral blood over 1.5 G/L, is clinical challenge in modern medicine [1]. A variety of causes and symptoms make patients undergo many tests before final diagnosis is made and the necessary therapy is initiated [1]. Factors predicting the final diagnosis might prove useful, as some of the more costly and invasive tests could be skipped [1]. The aim of the study was to find prognostic factors which may identify the cause of HE. Medical records of 39 patients with observed blood HE detected in at least one test who visited the Department of Allergology in Gdansk in the years 2010–2022 were analysed. In general, we supplemented the standard tests with additional ones when predicting neoplastic or autoimmune diseases. The peripheral blood morphology, serum biochemistry, parasitological examination, immunological studies (antineutrophil cytoplasmic antibodies (ANCA) test), additional tests, including the aspirin provocation test (performed in 46% of patients (n=18)), spirometry, histopathology and cytology of the bone marrow (done in 56% of patients (n=22)) were performed. The statistical analysis was conducted using binary logistic regression performed using Statistica 13 software.