From the Guidelines
Leukocytosis with a left shift is a strong indicator of a bacterial infection.
Key Findings
- The presence of an elevated WBC count (≥ 14,000 cells/mm³) or a left shift (percentage of band neutrophils or metamyelocytes, ≥ 16%; or total band neutrophil count, ≥ 1500 cells/mm³) warrants a careful assessment for bacterial infection in any resident with suspected infection, with or without fever 1.
- A left shift, characterized by an increased percentage of band neutrophils or metamyelocytes, has a high likelihood ratio for detecting documented bacterial infection 1.
- Leukocytosis with a left shift has been associated with increased mortality among residents with nursing home–acquired pneumonia and bloodstream infection 1.
Clinical Implications
- A complete blood cell count, including peripheral WBC and differential cell counts, should be performed for all residents who are suspected of having infection within 12–24 h of onset of symptoms 1.
- In the absence of fever, leukocytosis and/or left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may not be indicated due to the low potential yield 1.
- Nonbacterial infections, however, cannot be excluded based on these findings alone 1.
From the Research
Leukocytosis with a Left Shift
Leukocytosis with a left shift is a condition characterized by an increase in white blood cell count with a predominance of immature neutrophils in the peripheral blood. This condition can be an indicator of various diseases and infections.
- The presence of a left shift indicates an increase in neutrophil consumption that is equal to an increase in production 2.
- A left shift can be seen in bacterial infections, where large numbers of neutrophils are consumed, and the bone marrow mounts a response to the disease 3, 2, 4.
- Leukocytosis with a left shift can also be associated with severe COVID-19 infection, although more data are needed to evaluate this association 5.
- In addition to infectious diseases, leukocytosis with a left shift can be seen in other conditions such as trauma, autoimmunity, or diseases with significant tissue destruction 4.
- The extent of the left shift can be of differential diagnostic significance, and a careful microscopic assessment of a blood smear is required for qualitative interpretation of the differential blood count 6.
Diagnostic Implications
- Leukocytosis with a left shift can be an early pathological signal that may be seen during the course of numerous diseases 6.
- The presence of a left shift does not occur in the extremely early or late phases of infection, and assessing data from a single time point is unsuitable for diagnosing a bacterial infection 2.
- A degenerative left shift is considered a poor sign, indicating that the marrow has fallen somewhat behind the needs of the animal 4.
- Leukocyte evaluation should include not only total count and differential count but also morphologic examination of the cells by qualified people 4.