What is the significance of a reactive leukocyte (white blood cell) count?

From the Guidelines

A reactive leukocyte count is a significant indicator of the body's immune response to various stimuli, including infections, inflammation, or physiological stresses, and warrants careful assessment and interpretation in the context of clinical symptoms and other laboratory findings. Reactive leukocytes are white blood cells that show morphological changes, such as increased size, altered nuclear shape, cytoplasmic vacuolation, or the presence of toxic granulation, in response to these stimuli. According to the clinical practice guideline for the evaluation of fever and infection in older adult residents of long-term care facilities, a complete blood cell (CBC) count, including peripheral WBC and differential cell counts, should be performed for all residents suspected of having infection within 12–24 h of onset of symptoms 1.

The presence of an elevated WBC count (WBC count, ≥ 14,000 cells/mm³) or a left shift (percentage of band neutrophils or metamyelocytes, ≥ 16%; or total band neutrophil count, ≥ 1500 cells/mm³) warrants a careful assessment for bacterial infection in any resident with suspected infection, with or without fever 1. The evaluation of the total WBC count, number of band forms, and the percentage of neutrophils and band forms revealed that an elevated total band count (1500 cells/mm³) had the highest likelihood ratio for detecting documented bacterial infection 1.

Some key points to consider when interpreting reactive leukocytes include:

• Common causes of reactive leukocytes, such as bacterial or viral infections, inflammatory conditions, physical or emotional stress, certain medications, or recovery from recent surgery or trauma
• The importance of interpreting reactive leukocytes in the context of other laboratory findings and clinical symptoms, as they represent a non-specific finding that requires clinical correlation
• The need for careful assessment and potential further investigation to identify the underlying cause of persistent reactive leukocytes.

From the Research

Significance of Reactive Leukocyte Count

• A reactive leukocyte (white blood cell) count is a key parameter in establishing the diagnosis of sepsis and estimating its severity 2
• Leukocytosis, defined as a white blood cell count greater than 11,000/mcL in nonpregnant adults, is a common finding and can be caused by primary malignant diseases or secondary causes such as infections and chronic inflammatory conditions 3
• An increased white blood cell count can be evaluated based on which lineages are increased and the morphologic findings on peripheral blood smear review to guide further testing 4

Diagnostic Considerations

• A normal white blood cell count with a high C-reactive protein level can be seen in febrile patients with bacterial infections, and does not necessarily indicate an underlying malignant neoplasm or hematologic illness 5
• Neutrophil left shift and white blood cell count can be used as markers of bacterial infection, with dynamic changes in these parameters reflecting the severity of the infection 6
• The presence of blasts on a peripheral blood smear is concerning for acute leukemia and may require bone marrow biopsy 4

Clinical Implications

• Patients with chronic leukemias usually present with less severe symptoms than patients with acute leukemias, and symptoms generally are gradual in onset 3
• Acute leukemias should be recognized quickly because they may be associated with life-threatening complications, and urgent referral to a hematology subspecialist is indicated in cases of suspected acute leukemia 3
• Glucocorticosteroids can cause leukocytosis and neutrophilia, and this effect should be taken into consideration when using the level of leukocytosis as a parameter in the diagnosis of infectious processes 2