A left shift indicates the presence in blood of neutrophils less mature than segmented neutrophils, e.g. band neutrophils and earlier stages, such as metamyelocytes.
Cells of the neutrophil line are classified by the shape of their nuclei. Segmented neutrophils have nuclei with focal areas that are distinctly narrower than the width of the widest points (> 50%) and usually have irregular nuclear outlines. Cells with nuclei whose sides are parallel or nearly so (<50% indentation) or have smooth nuclear outlines are classified as band neutrophils. The band count includes more immature cells, such as metamyelocytes and myelocytes (for more information on these cells, refer to the leukocyte section of the hematology atlas). In the latter scenario, we usually flag the report to demonstrate the presence of cells more immature than bands.
The reference intervals for band neutrophils will be different from one laboratory to another due to differences in criteria used to classify a band from a segmented neutrophil (bands mature into segmented neutrophils so variants between these two stages may be seen). we found few to no band neutrophils in the blood of clinically healthy animals we used for our reference intervals, although this is species-dependent. This indicates that low numbers of bands, particularly in the absence of other features of inflammation, such as toxic change, may not be a clinically relevant finding.
The presence of increased numbers of bands (i.e. above the established reference interval for that species) or a left shift usually indicates a response to inflammatory cytokines, which are stimulating accelerated production and/or release of neutrophils. If more band neutrophils are counted than segmented neutrophils, the term degenerative left shift applies. This indicates severe inflammation in most species. In this setting, neutrophils demonstrate features of toxic change or immaturity (see image to the right). Also refer to the leukocyte section of the hematology atlas for more information on toxic change.
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