In shift to the left, there is a relative increase of band neutrophils compared to segmented neutrophils. The ratio is usually around 1to 4 (rule of filament) or 1 to 12-15 (rule of one third). In severe bacterial infections neutrophilic abnormalities such as toxic granulation, vacuoles and Döhle bodies are typically designated as toxic.
The (toxic) shift to the left is not a clinical picture but rather a descriptive morphological term. This blood film abnormality normally occurs in bacterial infections as well as in other situations such as in burns, tumor lysis or acute inflammation (e.g. a gout attack).
A leukocytosis with neutrophilia is usually present, which is explained by an increased release of immature neutrophils from the bone marrow. The leukocyte count is normally between 10-20x109/L. It may, however, be higher in certain cases. The disappearance of eosinophils is also typical. Normal leukocyte counts associated with toxic conditions can be a sign of an exhausted granulopoiesis, which indicates a distinct increase in peripheral consumption of neutrophils, as may be seen in sepsis.