The correct use of the term “left shift” refers to the presence of banded (immature) neutrophils in the blood. It does not refer to an elevated white blood cell count with a high percentage of neutrophils. An elevated white blood cell count with an abnormally high percentage of neutrophils should be called “neutrophillic leukocytosis.” Only the presence of immature neutrophils in the periphery (including bands) can accurately be called a “left shift.”
Almost immediately, emergency physicians know what to do with most abnormal lab results. If a patient’s hemoglobin is 4.5 g/dL, they need a transfusion. If their troponin is 12.3 ng/ml, they are having cardiac infarction. If their lactic acid is 7.5 mmol/L, something terrible is going on. What if the only abnormality they have on their blood work is bandemia? Does it matter if their bands are 6%, 15%, or 32%? Or, are they all treated equally?
WBC values vary depending on age, particularly in the early months of life, through childhood, and into adolescence. While gender differences are not observed, the WBC can vary with genetics, typically as a result of differences in specific cell lines.6 Thus, the use of the proper reference interval is especially important to the interpretation of WBC values. An increase above the reference interval is called leukocytosis while a decrease is leukopenia.
Leukemoid reaction is an uncommon clinical condition defined as leukocytosis >50,000 cells/mL with
predominantly mature neutrophils and accompanying left shift. It is known as a rare manifestation of
systemic inflammation or stress and has been reported in malignant and non-malignant disease processes. Coronavirus disease (COVID-19) has wide spectrum of clinical manifestations involving multiple
Leukocytosis, a common laboratory finding, is most often due to relatively benign conditions (infections or inflammatory processes). Much less common but more serious causes include primary bone marrow disorders. The normal reaction of bone marrow to infection or inflammation leads to an increase in the number of white blood cells, predominantly polymorphonuclear leukocytes and less mature cell forms (the “left shift”).
Leukocytosis may be an acute or chronic process. It is most
often caused by an appropriate physiologic response of normal bone marrow to an
infectious or inflammatory stimulus. Less frequently, leukocytosis is caused by a
primary bone marrow disorder, such as leukemia, lymphoma, or a myeloproliferative
Neutrophilic leukocytosis most often is reactive in nature in response to an infection or inflammatory process. Even total leukocyte counts of greater than 25,000 cells/mm3 (leukemoid reaction) pose no direct host threat. However, the one situation in which extreme leukocytosis (e.g., >100,000 cells/mm3) can be harmful or fatal is the hyperleukocytos-leukostasis syndrome associated with acute myeloid leukemia (AML).
Leukocytosis is the broad term for an elevated white blood cell (WBC) count, typically above 11.0x10^9/L, on a peripheral blood smear collection. The exact value of WBC elevation can vary slightly between laboratories depending on their 'upper limits of normal' as identified by their reference ranges.
Leukocyte count; White blood cell count; White blood cell differential; WBC differential; Infection - WBC count; Cancer - WBC count