Why is the White Blood Cell (WBC) count always mildly elevated?

From the Guidelines

A mildly elevated White Blood Cell (WBC) count is often a nonspecific indicator of an underlying inflammatory or infectious process, and its cause should be thoroughly investigated to rule out serious conditions, such as bacterial infections, which have been associated with increased mortality in certain populations 1. When evaluating a mildly elevated WBC count, it is essential to consider various potential causes, including:

• Chronic infections, such as tuberculosis or endocarditis
• Inflammatory conditions, like rheumatoid arthritis, lupus, or inflammatory bowel disease
• Physical or emotional stress, which can release cortisol and increase WBC production
• Certain medications, including corticosteroids, lithium, and some antibiotics
• Smoking, which can cause chronic inflammation and damage to lung tissue
• Blood disorders, such as leukemia or myeloproliferative disorders
• Obesity and pregnancy, which can also lead to mild elevations in WBC count According to a study published in the Clinical Infectious Diseases journal in 2009 1, a leukocyte count of 14,000 cells/mm3 had a likelihood ratio of 3.7 for indicating an underlying bacterial infection in older adults, highlighting the importance of further investigation in such cases. In clinical practice, a thorough evaluation, including a complete blood count with differential, medical history review, and possibly additional testing, is necessary to identify the underlying cause of a persistently elevated WBC count, especially if there are no obvious causes or if the patient belongs to a high-risk population, such as older adults residing in long-term care facilities 1.

From the Research

Possible Causes of Elevated White Blood Cell Count

• An elevated white blood cell count can have many potential etiologies, including malignant and nonmalignant causes 2
• Nonmalignant etiologies of leukocytosis include certain medications, asplenia, smoking, obesity, and chronic inflammatory conditions 2
• Stressors capable of causing an acute leukocytosis include surgery, exercise, trauma, and emotional stress 2
• Corticosteroids can cause leukocytosis, with the white blood cell count peaking at 48 hours after steroid administration 3

Relationship Between White Blood Cell Count and Infection

• Leukocytosis is a common sign of infection, particularly bacterial, and should prompt physicians to identify other signs and symptoms of infection 2
• A high C-reactive protein level and normal white blood cell count can be seen in febrile patients with bacterial infection 4
• Neutrophil left shift and white blood cell count can be used as markers of bacterial infection, with dynamic changes in these parameters reflecting the mild to serious condition of the infection 5

White Blood Cell Count Dynamics

• The white blood cell count can double within hours after certain stimuli due to the large bone marrow storage and intravascularly marginated pools of neutrophils 2
• The recovery trajectory of white blood cell count after inflammation is characterized by exponential decay, and can be used to identify high-risk patients 6
• The dynamics of white blood cell count and platelet count can provide a generic approach for identifying patients at risk of adverse outcomes 6