Eosinophilia is commonly observed in the haematology laboratory. It may be an important and often is the first indicator of the underlying problem. However, eosinophilia is like a mask behind which a multitude of different faces can be found. It can be associated with disparate diseases, including infective, allergic, immunologic, endocrine and neoplastic, or even exist in the absence of an apparent underlying pathology. It may persist in an innocent fashion or lead to irreversible organ damage. Eosinophilia can be reactive, clonal or a mix of the two. Consequently, eosinophilia has been subjected to many classifications in various fields of medicine including haematology. Although criteria and definitions have been overlapping, a degree of controversy and confusion has remained. Considerable advances in understanding the pathogenesis of eosinophilia and associated disorders, have been made recently, including the role of cytokines, chemokines and underlying molecular defects. This has led to a new era in the classification of these conditions. Proposals for a global multidisciplinary consensus for refining the criteria and merging prior classifications in a contemporary schema have been published.
The talk aims to cover the current definitions, criteria and classification of eosinophilic disorders and discuss diagnostic approach to patients presenting with persistent hypereosinophilia.