From the Guidelines
Leukocytosis, or an elevated white blood cell count, is typically caused by infections, inflammation, immune system disorders, bone marrow disorders, certain medications, or stress responses, with bacterial infections and bone marrow disorders being among the most significant causes, as seen in studies such as 1. When considering the causes of leukocytosis, it's essential to recognize the role of bacterial infections, which can lead to a significant increase in white blood cell count as the body responds to the invading pathogens. Inflammatory conditions, such as rheumatoid arthritis and inflammatory bowel disease, can also contribute to elevated white blood cell production. Additionally, immune disorders like allergic reactions and asthma may lead to an increase in specific types of white cells, particularly eosinophils.
Bone marrow disorders, including leukemia and certain lymphomas, directly affect white cell production, leading to leukocytosis. The most recent and highest quality study, 1, highlights the importance of understanding the criteria for accelerated and blast phases in chronic myeloid leukemia, which can help identify the underlying cause of leukocytosis. Medications such as corticosteroids, epinephrine, lithium, and colony-stimulating factors used during cancer treatment can also cause leukocytosis. Physical or emotional stress triggers cortisol release, which can temporarily increase white cell counts. Other factors, including smoking, excessive exercise, pregnancy, and splenectomy, may also contribute to elevated counts.
The specific pattern of which white cell types are elevated often provides clues to the underlying cause, making a complete blood count with differential an important diagnostic tool. For instance, a study from 1 discusses the management of hyperleukocytosis, which is a critical consideration in the context of leukemia and other bone marrow disorders. By understanding the various causes of leukocytosis and utilizing diagnostic tools like complete blood counts, healthcare providers can better identify and manage the underlying conditions contributing to elevated white blood cell counts.
Key causes of leukocytosis include:
- Bacterial infections
- Inflammatory conditions
- Immune system disorders
- Bone marrow disorders
- Certain medications
- Stress responses
- Other factors such as smoking, excessive exercise, pregnancy, and splenectomy.
From the Research
Causes of Leukocytosis
Leukocytosis, or an elevated white blood cell count, can be caused by a variety of factors, including:
- Infections or inflammatory processes, which are the most common causes of leukocytosis 2, 3, 4
- Physical stress, such as seizures, anesthesia, or overexertion 2
- Emotional stress 2
- Medications, including corticosteroids, lithium, and beta agonists 2
- Primary bone marrow disorders, such as acute leukemias, chronic leukemias, and myeloproliferative disorders 2, 3, 5, 4
- Allergic reactions, which can cause an increase in eosinophil or basophil counts 2
- Autoimmune disorders, such as rheumatoid arthritis, which can cause leukocytosis due to disease activity or steroid therapy 6
Primary Bone Marrow Disorders
Primary bone marrow disorders, such as leukemias, can cause leukocytosis due to an overproduction of white blood cells. These disorders can be acute or chronic, and may present with symptoms such as weight loss, bleeding or bruising, liver, spleen or lymph node enlargement, and immunosuppression 2, 4.
- Acute leukemias, such as acute myeloid leukemia (AML), can present with extremely elevated white blood cell counts and may be associated with life-threatening complications such as leukostasis, disseminated intravascular coagulation (DIC), and tumor lysis syndrome (TLS) 5
- Chronic leukemias, such as chronic lymphocytic leukemia (CLL), may present with less severe symptoms and may be diagnosed incidentally due to abnormal blood cell counts 2, 4
Secondary Causes
Secondary causes of leukocytosis, such as infections and inflammatory conditions, are expected physiologic responses of the bone marrow. These causes can be identified through a thorough history, physical examination, and peripheral blood smear 4.