Definition

• • Absolute neutrophil count <2000/μL (increased risk of bacterial infection with count <1000/μL).

Pathophysiology

• • decreased production or increased peripheral destruction.

Causes

• 1. Drugs—cancer chemotherapeutic agents are most common cause, also phenytoin, carbamazepine, indomethacin, chloramphenicol, penicillins, sulfonamides, cephalosporins, propylthiouracil, phenothiazines, captopril, methyldopa, procain- amide, chlorpropamide, thiazides, cimetidine, allopurinol, colchicine, ethanol, penicillamine, and immunosuppressive agents;

  2. infections—viral (e.g., influenza, hepatitis, infectious mononucleosis, HIV), bacterial (e.g., typhoid fever, miliary tuberculosis, fulminant sepsis), malaria;

  3. nutritional—B12, folate deficiencies;

  4. benign—benign ethnic neutropenia (BEN) seen in up to 25% of blacks, no associated risk of infection;

  5. hematologic diseases—cyclic neutropenia (q21d, with recurrent infections common), leukemia, myelodysplasia (preleukemia), aplastic anemia, bone marrow infiltration (uncommon cause), Chédiak-Higashi syndrome;

  6. hypersplenism—e.g., Felty’s syndrome, congestive splenomegaly, Gaucher’s disease;

  7. autoimmune diseases—idiopathic, SLE, lymphoma (may see positive antineutrophil antibodies);

  8. genetics—inheritance of an allele of the Duffy antigen receptor for cytokines (DARC) can be associated with constitutive neutropenia that is not associated with predilection to infection; more common in African Americans.