What does a "left shift" on a CBC indicate?

A "left shift" on a Complete Blood Count (CBC) refers to an increased number of immature white blood cells, particularly neutrophil precursors, in the bloodstream. This typically indicates that the body is responding to an infection or inflammation. When the bone marrow is stimulated to produce more white blood cells to fight off pathogens, it releases these immature cells before they fully mature. This phenomenon supports the body's defense mechanisms against infections or other serious conditions.

The presence of immature cells is significant in clinical diagnosis, as it helps healthcare practitioners assess the underlying cause of an elevated white blood cell count and the body's response to stressors. Recognizing a "left shift" can guide further diagnostics and treatment interventions.