Eosinophils > 1.5 × 109/L in blood on 2 examinations (interval > 1 month) and/or tissue HE defined by the following:1. Percentage of eosinophils in BM section exceeds 20% of all nucleated cells and/or2. Pathologist is of the opinion that tissue infiltration by eosinophils is extensive and/or3. Marked deposition of eosinophil granule proteins is found (in the absence or presence of major tissue infiltration by eosinophils). This evidence concerns the gene PROS1 and hereditary elliptocytosis.