When you’re faced with an acute leukemia composed entirely of blasts, one way to figure out the identity of those blasts is to use cytochemical stains. These stains are applied to slides – either smears (blood or bone marrow) or sections (of bone marrow) – and are read under the microscope. There are several different cytochemical stains that are commonly used in hematopathology, one of which is the non-specific esterase (or NSE) stain. Monocytes and their precursors (promonoblasts and monoblasts) stain a pretty red color with this stain. Neutrophils and their precursors (including myeloblasts), and most of the other types of cells in the bone marrow (except cells of the megakaryocytic lineage, which are sometimes positive), are negative.

So if you have a leukemia composed of a sea of undifferentiated blasts, you could stain the blood or marrow smears (or the bone marrow section, though it’s harder to see individual cell morphology on a section) with NSE. If the cells stain red, then you’re probably dealing with a leukemia composed of monocytic cells – probably a monoblastic leukemia, if all you’re seeing is blasts. It’s a quick and easy way to help you diagnose the leukemia.