Clinical meaning
Neutropenia is defined as an absolute neutrophil count (ANC) below 1500 cells per microliter (1.5 x 10^9/L). Neutrophils are the most abundant type of white blood cell, comprising 55-70% of circulating leukocytes, and serve as the first line of defense against bacterial and fungal infections. They are produced in the bone marrow from myeloid stem cells through a process called granulopoiesis, which takes approximately 10-14 days from stem cell to mature neutrophil. Neutrophils circulate in the blood for only 6-10 hours before migrating into tissues, where they survive for 1-2 days performing phagocytosis -- the process of engulfing and destroying pathogens. The absolute neutrophil count is calculated using the formula: ANC = WBC x (percentage of neutrophils + percentage of bands) / 100. Bands are immature neutrophils released from the bone marrow; an elevated band count (bandemia or left shift) indicates the bone marrow is attempting to compensate for increased demand during infection. Neutropenia is classified by severity: mild (ANC 1000-1500), moderate (ANC 500-1000), and severe (ANC below 500). Severe neutropenia (ANC below 500) carries the highest risk for life-threatening...