Medical Definition of Neutrophil. Neutrophil: A type of white blood cell, a granulocyte that is filled with microscopic granules, little sacs containing enzymes that digest microorganisms. Also known as polymorphonuclear leukocyte or poly.
Definition of Neutropenia. Neutropenia: Not enough neutrophils, neutrophils being a type of white blood cell (specifically a form of granulocyte) filled with neutrally-staining granules, tiny sacs of enzymes that help the cell to kill and digest microorganisms it has engulfed by phagocytosis.
Neutrophils are a common type of white blood cell important to fighting off infections â particularly those caused by bacteria. For adults, counts of less than 1,500 neutrophils per microliter of blood are considered to be neutropenia. For children, the cell count indicating neutropenia varies with age. Some people have lower-than-average neutrophil counts, but not an increased risk of infection. In these situations their neutropenia isn't a concern.