Non-specific esterases most often occur in monocytes, megakaryocytes and platelets.
Non-specific esterases produce an orange-brown stain in positive cases. Monocytes and macrophages show the strongest reaction. Granulopoietic cells do not react. In the case of T-lymphocytes, dot-like precipitates can occur.
Non-specific esterase is primarily used to differentiate myelomonocytic leukemia (M4 according to FAB) and monocytic leukemia (M5 according to FAB) from other acute myelocytic leukemias. It is also helpful in monocytosis especially in chronic myelomonocytic leukemia.