see also:

• full blood examination (FBE)
• neutrophilia
• monocytosis
• lymphopenia
• lymphadenopathy

• the finding of a raised WCC due to lymphocytosis rather than neutrophilia is generally a reassuring find which suggests viral infection rather than bacterial infections although it is a typical finding in pertussis (whooping cough)
• atypical lymphocytes suggests viral infections including EBV / glandular fever / infectious mononucleosis
• a very high count or abnormal lymphocytes suggests chronic lymphocytic or acute lymphoblastic leukaemia

• viral infections
• pertussis (whooping cough)
• toxoplasmosis
• tuberculosis (TB)
• brucellosis
• asplenia
• monoclonal B-cell lymphocytosis (MBL)
  • affects ~3% of those aged > 40yrs; 1-5 monoclonal lymphocytes/microL
  • may be a precursor to chronic lymphocytic leukemia (CLL) and, like CLL, has increased risks for developing melanoma
• lymphoma
• chronic lymphocytic leukemia
  • usually have > 5000 monoclonal lymphocytes/microL blood
• acute lymphoblastic leukemia
• smokers
• American trypanosomiasis (Chagas disease)