Neutropenia is defined as a decrease in the blood neutrophil count below 1.5 × 109/ L. In some racial groups (e.g., Africans), the normal neutrophil count is somewhat lower (up to 1.2 × 109/L). While mild neu-tropnia may be asymptomatic, severe neu-tropenia (counts < 0.5 × 109/L) is invariably associated with the risk of life-threatening microbal sepsis caused by a broad range of endogenous Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli, Pseudomonas spp., Klebsiella spp.) as well as fungi (Candida). Neutrophils are particu-larly important for maintaining the integ-rity of mucous membranes. Hence, oral ulceration and perianal inflammation can be features of severe neutropenia. Causes of neutropenia are summarized in Table 5.7.
Table 5.7 Causes of Neutropenia