Lymphocytosis
Last updated Nov. 3, 2025, 5:56 a.m. by ivo
Tags: Lymphocytosis , chronic lymphocytic leukemia , lymphoma
Causes
- Isolated lymphocytosis is common and usually seen in response to viral or other atypical infections.
- Cigarette smoking and hyposplenic states are also implicated.
- Lymphocytosis may also be associated with transient stressors, e.g. myocardial infarction, trauma, obstetric complications, seizures, vigorous exercise.
- The most common neoplastic cause is chronic lymphocytic leukaemia (CLL), which may present as an isolated lymphocytosis (>5x109/L) or as a lymphoma-type picture with lymphadenopathy, cytopenias and constitutional symptoms. Peripheral blood flow cytometry is the most useful initial investigation to exclude a lymphoproliferative disorder such as CLL.
Investigations
- Clinical history and examination to assess for unintentional weight loss, night sweats, enlarging nodes, hepatosplenomegaly and intercurrent illness such as infection.
- Full blood count to assess for anaemia, thrombocytopenia, neutropenia.
- Blood film to assess lymphocyte morphology.
- ELFTs to assess albumin and LDH.
- Serology as clinically indicated e.g. pertussis, EBV, CMV, influenza, hepatitis A.
- Following an initial finding of an elevated lymphocyte count, it is reasonable to repeat the blood count in 4-6 weeks to assess progress.
- If the lymphocytosis persists and there is no apparent secondary cause, peripheral blood flow cytometry can be performed to assess for an aberrant or clonal population.
- The lymphocytosis is unlikely to be caused by a haematological condition if flow cytometry is normal.
Follow up
If flow cytometry is normal and there are no associated B symptoms, cytopenias or lymphadenopathy, it is reasonable to repeat the lymphocyte count every 3-6 months, while also assessing for other potential underlying causes.0 comments
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