From the Guidelines
Reactive leukocytosis refers to a temporary increase in white blood cell count that occurs as a normal physiological response to various stressors or conditions in the body, such as infection, inflammation, or physical stress, as seen in conditions like Kawasaki disease 1. This elevation is not due to a primary blood disorder but rather represents the immune system's reaction to infection, inflammation, physical or emotional stress, certain medications, or other stimuli. During reactive leukocytosis, the bone marrow increases production of white blood cells, particularly neutrophils, to help fight infection or respond to inflammation. Common causes include bacterial infections, tissue damage from burns or surgery, severe exercise, seizures, acute hemorrhage, and certain medications like corticosteroids or epinephrine. Some key points to consider when evaluating reactive leukocytosis include:
- The condition typically resolves once the underlying cause is addressed.
- Reactive leukocytosis is distinguished from pathological leukocytosis (such as in leukemia) by its temporary nature and normal white blood cell morphology.
- Normal white blood cell counts range from 4,500 to 11,000 cells per microliter, with counts above this range potentially indicating reactive leukocytosis depending on the clinical context, as noted in studies on adult onset Still's disease 1 and the evaluation of fever and infection in older adult residents of long-term care facilities 1. It is essential to consider the clinical context and underlying cause of the leukocytosis to provide appropriate management and prevent potential complications.
From the Research
Definition of Reactive Leukocytosis
- Reactive leukocytosis refers to an increase in the white blood cell (WBC) count in response to a non-malignant stimulus, such as infection, inflammation, or trauma 2, 3.
- This condition is characterized by an elevated WBC count, which can be divided into myeloid and lymphoid processes 2.
- Reactive leukocytosis can be distinguished from malignant leukocytosis by examining the morphology of the WBCs and the presence of blasts or other abnormal cells 2, 3.
Causes of Reactive Leukocytosis
- Infections, such as pneumonia, urinary tract infections, and abscesses, are common causes of reactive leukocytosis 4.
- Other causes include trauma, inflammation, and certain diseases, such as chronic lymphocytic leukemia 4, 5.
- Reactive leukocytosis can also be induced by certain medications, such as antibiotics 6.
Characteristics of Reactive Leukocytosis
- Reactive leukocytosis is often characterized by an increase in neutrophils, eosinophils, or basophils, depending on the underlying cause 2, 3.
- The WBC count can range from mildly elevated to extremely high, depending on the severity of the underlying condition 4.
- Reactive leukocytosis can be associated with other laboratory findings, such as anemia, thrombocytosis, or elevated inflammatory markers 5.