NeutrophilsNeutrophil count · ANC
The most numerous white cells, and the first responders to bacterial infection.
Neutrophils are the largest group of white blood cells and the immune system's front line. They arrive first at sites of infection or injury and engulf bacteria directly.
It matters in both directions. The count rises quickly with bacterial infection, tissue damage, physical stress and steroid medication, and a genuinely low count leaves someone more vulnerable to infection.
In practice neutrophils rise sharply and briefly after hard exercise, so a sample taken soon after training can look inflammatory when nothing is wrong. It is read as part of the full white cell differential.