Incidental finding of lymphocytosis in an asymptomatic patient -- Grove et al. 338: b2119 -- BMJ

Causes of lymphocytosis

Reactive (secondary) lymphocytosis

Normal morphology

• Chronic smoking
• Acute hypoxia (transient):

  Acute asthma

  Pulmonary embolus

  Myocardial infarction

• Acute stress (transient)
• Bordetella pertussis

Atypical morphology

• Viral infections:

  Most common—Epstein-Barr virus; cytomegalovirus

  Less common—herpes simplex, influenza, mumps, HIV, dengue haemorrhagic fever; hepatitis A or B

• Bacterial infections:
• • Rickettsial infections
• Drug hypersensitivity

Neoplastic (primary) lymphocytosis

• Chronic lymphocytic leukaemia—most common
• Less common neoplasms:

  Hairy cell leukaemia

  Prolymphocytic leukaemia

  Leukaemic phase of non-Hodgkin lymphoma

Summary of the article

• Lymphocyte morphology can often distinguish between reactive and neoplastic causes of lymphocytosis
• If "atypical lymphocytes" are present, an infectious mononucleosis screening test and viral serology are indicated
• If the lymphocytes have normal morphology and the cause of lymphocytosis is uncertain, repeat the blood count and film in 2-4 weeks
• When lymphocytosis is persistent and unexplained, lymphocyte phenotyping may provide insight into the aetiology

Incidental finding of lymphocytosis in an asymptomatic patient -- Grove et al. 338: b2119 -- BMJ