The Absolute Neutrophil Count (ANC) is a crucial laboratory marker that reflects the body’s ability to fight bacterial and fungal infections. Neutrophils, a type of white blood cell, play a frontline role in the immune response by engulfing and destroying pathogens. Low neutrophil levels, known as neutropenia, can occur due to chemotherapy, bone marrow disorders, autoimmune diseases, certain medications, or severe infections. Monitoring ANC allows clinicians to identify patients at increased risk of life-threatening infections, guiding decisions about prophylaxis, isolation measures, and treatment modifications.

ANC is particularly important in oncology, where chemotherapy often suppresses bone marrow function. Patients with severe neutropenia are vulnerable to opportunistic infections and require prompt medical attention at the first signs of fever. The test is also valuable in diagnosing bone marrow failure syndromes, monitoring response to therapy, and evaluating the severity of acute or chronic illness.

Interpretation of ANC levels typically follows risk thresholds that stratify patients from normal immune function to severe neutropenia. Clinical context, including symptoms and comorbidities, must be considered alongside the raw number. For instance, a stable outpatient with mild neutropenia may only need observation, whereas a febrile inpatient with the same count may require urgent hospitalization and antibiotics.