From the Guidelines
A left shift in a CBC is a critical indicator of an active infection or inflammatory process, characterized by an increased number of immature neutrophils in the bloodstream, and is defined as a percentage of band neutrophils or metamyelocytes ≥ 16% or a total band neutrophil count ≥ 1500 cells/mm³, as per the guidelines outlined by the Infectious Diseases Society of America 1. This occurs when the bone marrow releases immature neutrophils prematurely to help fight an infection before they have fully matured. The term "left shift" comes from the traditional manual method of recording blood cell counts, where immature cells were tallied on the left side of the differential count sheet. Common causes of a left shift include:
- Bacterial infections
- Inflammation
- Tissue damage
- Certain medications
- Some cancers A left shift is clinically significant because it suggests the body is actively responding to an infection or inflammatory stimulus. The presence and degree of a left shift can help guide diagnosis and treatment decisions, particularly regarding the need for antibiotics in suspected bacterial infections, with studies demonstrating a high probability of an underlying bacterial infection in older persons with an elevated WBC count, high percentage of neutrophils, or left shift, even in the absence of fever 1. However, the finding should always be interpreted in the context of the patient's clinical presentation and other laboratory values. In clinical practice, a CBC count, including peripheral WBC and differential cell counts, should be performed for all suspected infections, and the presence of a left shift warrants a careful assessment for bacterial infection 1.
From the Research
Definition of Left Shift in CBC
- A left shift in a Complete Blood Count (CBC) refers to an increase in the number of immature neutrophils, specifically band neutrophils, in the blood [ 2 ].
- This occurs when the bone marrow releases more immature neutrophils into the bloodstream in response to an increased demand, often due to infection or inflammation.
Causes of Left Shift
- Bacterial infections are a common cause of left shift, as the body tries to fight off the infection by producing more neutrophils [ 2 ].
- Other conditions, such as severe inflammation, trauma, or burns, can also cause a left shift.
- A left shift can be seen in various diseases, including cardiovascular and metabolic diseases, as indicated by changes in CBC components [ 3 ].
Interpretation of Left Shift
- A left shift is often accompanied by an increase in white blood cell (WBC) count, which can indicate the presence of an infection or inflammation [ 2 ].
- The presence of a left shift, along with other CBC components, can be useful in diagnosing and monitoring various medical conditions [ 4, 5 ].
- Neutrophils play a crucial role in fighting infections, and their biology is essential in understanding the left shift [ 6 ].