A normal mature neutrophil is 10–15 µm in diameter and contains 3–5 lobes or segments. The cell is hypersegmented when the number of segments is increased to six or more. Some hypersegmented cells will be larger than 15 microns. Hypersegmentation is seen most frequently in neutrophils but can also occur in eosinophils and basophils.
The nuclear segments are composed of deoxyribonucleic acid (DNA). A defect in the production of DNA causes the maturation process to be slower than normal, which in turn causes the nucleus to hypersegment. The cytoplasm will be normal in appearance and function, indicating that these cells can be phagocytosed. These cells are considered pathological.
