From the Guidelines
A left shift on a Complete Blood Count (CBC) is a significant indicator of an active inflammatory process, typically seen in bacterial infections, severe inflammation, tissue damage, or certain malignancies, and should prompt further investigation for underlying infection or inflammation, as recommended by the Infectious Diseases Society of America 1.
Definition and Clinical Significance
A left shift refers to an increased number of immature neutrophils (band cells) in the peripheral blood, indicating that the bone marrow is releasing these cells prematurely in response to infection or inflammation. This occurs when the demand for neutrophils exceeds the supply of mature cells, prompting the release of immature forms. The term "left shift" comes from the traditional manual differential count where immature cells were recorded on the left side of the worksheet.
Diagnostic Approach
When evaluating a left shift, it's essential to consider the total white blood cell count as well, as a left shift with leukocytosis (elevated white blood cells) typically indicates infection, while a left shift with normal or low white blood cells may suggest bone marrow suppression with ongoing inflammation. 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 LTCF resident with suspected infection, with or without fever, as stated in the clinical practice guideline for the evaluation of fever and infection in older adult residents of long-term care facilities 1.
Key Considerations
- A complete blood cell count, including peripheral WBC and differential cell counts, should be performed for all LTCF residents who are suspected of having infection within 12–24 h of onset of symptoms (or sooner, if the resident is seriously ill) 1.
- The degree of left shift can sometimes correlate with the severity of infection.
- 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, because of the low potential yield (C-III), but nonbacterial infections cannot be excluded 1.
Recommendations
- A left shift should prompt further investigation for underlying infection or inflammation, and a careful assessment for bacterial infection should be performed in any LTCF resident with suspected infection, with or without fever 1.
- Consider the total white blood cell count when evaluating a left shift, as a left shift with leukocytosis typically indicates infection, while a left shift with normal or low white blood cells may suggest bone marrow suppression with ongoing inflammation.
From the Research
Left Shift on CBC
- A left shift on a complete blood count (CBC) refers to an increase in the number of immature white blood cells, particularly neutrophils, in the blood [(2,3)].
- This can be an indication of a bacterial infection, as the body produces more white blood cells to fight off the infection [(2,3)].
- The combination of white blood cell count and left shift can be used to reflect the course of a bacterial infection, with different phases of infection corresponding to different levels of white blood cell count and left shift 2.
- A decrease in white blood cell count with a left shift can indicate that neutrophil consumption is surpassing supply, while an increase in white blood cell count with a left shift can indicate an increase in neutrophil production 3.
Causes of Left Shift
- Bacterial infections are a common cause of left shift, as they stimulate the production of white blood cells [(2,3,4)].
- Other causes of left shift include physical stress, emotional stress, and certain medications such as corticosteroids, lithium, and beta agonists 4.
- Primary bone marrow disorders, such as leukemia, can also cause left shift, particularly if the white blood cell count is extremely elevated 4.
Clinical Significance
- Left shift can be an important indicator of the severity of a bacterial infection, with more significant left shift indicating a more serious infection 3.
- Time-series data of left shift and white blood cell count can provide a more accurate evaluation of patient condition, allowing for more effective treatment 3.
- Extremely elevated white blood cell counts can represent a medical emergency, particularly if there are concurrent abnormalities in red blood cell or platelet counts 4.