Benign ethnic neutropenia: mild (ANC>1000), chronic, usually in patients with Mediterranean or African ancestry
Benign familial neutropenia: same as above, but hereditary and not associated with a specific ethnicity
Cyclic neutropenia: hereditary, with severe neutropenia on a 21-day cycle since childhood
Others: severe congenital neutropenia, Schwachman-Diamond syndrome, Fanconi anemia, dyskeratosis congenita, Chediak-Higash syndrome, myelokathesis, Griscelli syndrome II, and cartilage-hair hypoplasia
Acquired
Infectious
Active infection, particularly viral, but including severe sepsis from any cause; more common in the elderly
Post-infectious neutropenia, most commonly in children after viral infections (particularly varicella, measles, rubella, influenza, hepatitis, EBV, or HIV)
EBV and HIV can sometimes cause prolonged neutropenia; the rest are self-limited