From the Guidelines
A left shift in white blood cell count is defined as an increased number of immature neutrophils, such as bands, metamyelocytes, and myelocytes, in the peripheral blood, typically indicated by a percentage of band neutrophils or metamyelocytes of 16% or higher, or a total band neutrophil count of 1500 cells/mm³ or higher, as stated in the 2009 clinical practice guideline for the evaluation of fever and infection in older adult residents of long-term care facilities 1.
Definition and Clinical Significance
A left shift occurs when the bone marrow releases these immature cells prematurely in response to increased demand, typically during acute bacterial infections, inflammation, or other physiological stresses. Normally, neutrophils complete their maturation in the bone marrow before entering circulation, but during a left shift, this process is accelerated to meet the body's increased need for white blood cells to fight infection.
Key Points to Consider
- The term "left shift" originates from the traditional manual differential count, where immature cells were recorded on the left side of the laboratory form.
- A left shift is clinically significant as it often indicates an active infection or inflammatory process requiring medical attention.
- The presence and degree of a left shift can help clinicians assess the severity of an infection and monitor response to treatment, as noted in the study published in Clinical Infectious Diseases in 2000 1 and further emphasized in the 2009 update by the Infectious Diseases Society of America 1.
Clinical Application
In clinical practice, the presence of a left shift, along with other clinical manifestations and laboratory findings, such as an elevated WBC count, should prompt a careful assessment for bacterial infection, even in the absence of fever, as recommended in the clinical practice guidelines 1.
From the Research
Definition of Left Shift
- The left shift, also known as a neutrophil left shift, refers to an increase in the number of immature neutrophils (such as band cells) in the blood, which can be an indicator of infection or inflammation 2, 3.
- It is commonly used as an adjunct to the early diagnosis of bacterial infection, and can be quantified using various methods such as the absolute band count, band/seg ratio, band/total neutrophil ratio, and immature/total neutrophil ratio 2.
- A left shift can occur when the body needs to increase its production of neutrophils to fight an infection, and can be reflected in changes in the white blood cell (WBC) count and differential count 3.
Context of White Blood Cell (WBC) Count
- In the context of WBC count, a left shift indicates an increase in neutrophil consumption that is equal to an increase in production, and can be a sign of bacterial infection 3.
- The presence of a left shift, along with an elevated WBC count, can be a strong indicator of infection or inflammation 4, 5.
- However, it's worth noting that a left shift can also be caused by other factors, such as Pelger-Huet anomaly, a benign genetic condition that affects the shape of neutrophils 4.
Diagnostic Value
- The diagnostic value of the neutrophil left shift in predicting inflammatory and infectious disease has been evaluated in several studies, with mixed results 5, 6.
- Some studies have found that the band count is a useful indicator of infection, particularly in certain populations such as the elderly and infants 5, 6.
- However, other studies have found that the diagnostic value of the left shift is limited, and that other parameters such as the absolute neutrophil count and toxic granulation may be more sensitive and specific indicators of infection 5, 6.