A complete blood count (CBC) with differential provides information about the different types of white blood cells in a person’s blood. The “bands” or band neutrophils, represent immature neutrophils. Determining the percentage or absolute count of these cells involves manual or automated laboratory techniques. Typically, automated hematology analyzers count various cell populations. The percentage of bands is then either directly measured by the analyzer (in more advanced instruments) or determined manually by a trained technician examining a peripheral blood smear under a microscope, counting the number of bands relative to the total number of neutrophils or total white blood cells. The absolute band count is then calculated by multiplying the percentage of bands by the total white blood cell count.
Elevated band counts, a condition known as bandemia or a “left shift,” can be a significant indicator of infection, inflammation, or other hematologic disorders. Tracking these values is clinically relevant because it provides insight into the body’s immediate response to challenges in the blood.Historically, evaluating band counts was a critical component of diagnosing and monitoring bacterial infections before rapid diagnostic testing became widely available. While advanced techniques offer more specific markers of infection, assessment of band counts remains a readily accessible and useful tool, particularly in resource-limited settings or when a comprehensive differential count is already being performed.
