From the Guidelines
A left shift, in the context of a complete blood cell count, refers to an increase in the percentage of immature neutrophils, such as band neutrophils or metamyelocytes, which is a sign of a potential bacterial infection. This is often defined as a percentage of band neutrophils or metamyelocytes of 16% or higher, or a total band neutrophil count of 1500 cells/mm³ or higher 1. The presence of a left shift, along with an elevated white blood cell (WBC) count, is a significant indicator of bacterial infection, particularly in older adults residing in long-term care facilities 1. Key points to consider when evaluating a left shift include:
- The percentage of band neutrophils or metamyelocytes should be 16% or higher to be considered a left shift 1
- The total band neutrophil count should be 1500 cells/mm³ or higher to be considered a left shift 1
- A left shift, in combination with an elevated WBC count, warrants a careful assessment for bacterial infection, even in the absence of fever 1 It is essential to note that the evaluation of a left shift should be done in the context of the patient's overall clinical presentation, including symptoms, medical history, and other laboratory results 1.
From the Research
Definition of Left Shift
- A left shift, also known as a leukocyte left shift, refers to an increase in the number of immature white blood cells, particularly neutrophils, in the bloodstream 2, 3, 4.
- This occurs when the bone marrow releases more immature cells into the circulation in response to an increased demand for neutrophils, often due to infection or inflammation 2, 5.
Causes of Left Shift
- Bacterial infections are a common cause of left shift, as the body attempts to fight off the infection by producing more neutrophils 2, 4.
- Other causes of left shift include physical stress, emotional stress, and certain medications such as corticosteroids, lithium, and beta agonists 5.
- Primary bone marrow disorders, such as leukemia, can also lead to an increased number of immature white blood cells in the bloodstream 5.
Characteristics of Immature Neutrophils
- Immature neutrophils, also known as band forms, are capable of mediating important innate immune functions such as bacterial phagocytosis and killing 6.
- However, they are less efficient than mature neutrophils and have a longer life span and resistance to spontaneous apoptosis 6.
- Immature neutrophils also express lower levels of receptors for bacterial molecules and migrate less efficiently than mature granulocytes 6.
Clinical Significance of Left Shift
- A left shift can be an indicator of bacterial infection, particularly in newborn infants 2.
- The degree of left shift can also serve as a method for detecting subjects at high risk for depletion of the marrow neutrophil reserves and death from sepsis 2.
- However, a left shift can also be caused by other factors, such as Pelger-Huet anomaly, a benign genetic disorder 3.