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How does a differential white blood cell count help identify possible infections?
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blood disease
Peripheral blood smear revealing histopathologic features indicative of a blast crisis in a case of chronic myelogenous leukemia (CML). Blast crisis occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells, or blast cells. This phase of CML is characterized by fever, weakness, and an enlarged spleen.
A differential white blood cell count helps identify possible infections by measuring the percentage of each specific type of white blood cell in the blood. Because different cells perform specialized roles in the immune system, abnormal values for specific cell types can point toward the nature of an underlying infection.123
Key indicators include:
- Neutrophils: An increase in the percentage of band (immature) neutrophils is often associated with bacterial infections. Generally, an increase in granulocytes, particularly neutrophils, is a common response to pyogenic (pus-producing) organisms.34
- Lymphocytes: An increase in the number of small lymphocytes, known as lymphocytosis, is typically indicative of a viral origin. Conversely, specific viral infections, such as infectious mononucleosis, may present with unusually large, atypical lymphocytes.24
- Eosinophils: Elevated levels of eosinophils are characteristic of parasitic infections and allergic conditions.43
- Monocytes: An increase in monocytes, or monocytosis, is often associated with subacute bacterial endocarditis and malaria.4
By analyzing which cell populations are elevated or depressed, clinicians can better narrow down the potential cause of an infection.23