How I investigate difficult cells at the optical microscope.

Blood cell morphological identification on the peripheral blood and bone marrow films remains a cornerstone for the diagnosis of hematological neoplasms to be integrated with immunophenotyping, molecular genetics, and histopathology. Although standardization is still far from being achieved, with high interobserver variability, in recent years, several classification approaches, from the 1976 FAB to the 2016 WHO classification, have provided hematologists with detailed morphological descriptions for a large number of diseases. Counting blasts and detecting dysplastic specimens are two cornerstones of morphological diagnosis. This review deals with identifying difficult cells, with particular reference of those with relevant diagnostic implications.