From the Guidelines
An increase in lymphocytes, also known as lymphocytosis, is typically indicated by a sustained increase of peripheral blood lymphocytes ≥ 5 · 109 cells/l not explained by other clinical disorders, as stated in the study by 1. This condition can be a response to various factors, including:
- Infections, such as viral infections like Epstein-Barr virus, cytomegalovirus, hepatitis, or HIV, and bacterial infections like pertussis
- Certain cancers, particularly lymphomas and lymphocytic leukemias
- Autoimmune disorders
- Reactions to certain medications Normal lymphocyte counts generally range from 1,000 to 4,800 cells per microliter in adults. When lymphocytes increase significantly above this range, further investigation is warranted to determine the underlying cause. The pattern and type of lymphocytes elevated (T cells, B cells, or natural killer cells) can provide additional diagnostic information. Persistent unexplained lymphocytosis requires medical evaluation, as it may represent either a temporary response to infection or a more serious underlying condition requiring specific treatment, as noted in the study by 1. It is essential to consider the criteria for initiating treatment, such as evidence of progressive marrow failure, massive or progressive splenomegaly, massive nodes, or progressive lymphocytosis with an increase of more than 50% over a 2-month period, as outlined in the study by 1. In the context of chronic lymphocytic leukemia (CLL), the diagnosis is established by a combination of criteria, including a sustained increase of peripheral blood lymphocytes, predominance of small, morphologically mature lymphocytes, and specific immunophenotyping results, as described in the study by 1. The study by 1 provides the most recent and highest quality evidence for the diagnosis and treatment of CLL, and its recommendations should be prioritized in clinical practice.
From the Research
Indicators of Increased Lymphocytes
- Lymphocytosis, which is an increase in the total number of lymphocytes, can be indicated by various factors, including infectious mononucleosis and cytomegalovirus infection 2
- A reactive lymphocytosis is commonly associated with many viral and certain bacterial infections, which can lead to an increase in lymphocytes 2
- The presence of lymphoma cells or abnormal cells such as blast cells in the blood can also indicate an increase in lymphocytes, but this may be associated with malignant conditions 3
- Benign lymphocytosis can occur in response to viral infections, autoimmune diseases, or drug-related reactions, and can be characterized by a pleomorphic appearance of lymphocytes 3
Conditions Associated with Increased Lymphocytes
- Infectious mononucleosis, which is characterized by a massive lymphocytosis, can be caused by Epstein-Barr Virus (EBV) infection 4
- Systemic autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, have been linked to chronic or recurrent EBV infection 4
- Metabolic dysregulation of lymphocytes can contribute to the pathogenesis of autoimmune diseases, and may be associated with an increase in lymphocytes 5
- Viral infections can influence lymphocyte metabolism and lead to changes in lymphocyte function and numbers 6