There are two main categories that inhibit the production of neutrophils, and things that remove neutrophils from the circulation.
Things that inhibit the production of neutrophils:
- Hematopoietic stem cell suppression (e.g., aplastic anemia, infiltrative bone marrow diseases). Note: in these settings, you'd see anemia and thrombocytopenia too (good diagnostic clues).
- Drug reaction (This is the most common cause of neutropenia! The list of drugs is looooong; check out Robbins page 582.)
- Ineffective hematopoiesis (like that seen in megaloblastic anemia and myelodysplasia).
- Congenital disorders (rare, rare, rare) like Kostmann syndrome, in which patients have defects in genes involved in granulocyte differentiation.
Things that remove neutrophils from the circulation:
- Immunologic processes (like lupus, or drug exposure).
- Splenomegaly (a big spleen sequesters neutrophils - as well as red cells and platelets).
- Overwhelming infection (the patient is using up all the neutrophils by calling them out of the blood into the tissues).
For more on causes of neutropenia, see Robbins Pathologic Basis of Disease ("big Robbins") 9th edition, page 582 (or 8e, page 593).
