Last updated: Monday, 20, December, 2010
Key InformationAppropriate Tests

Review clinical findings, FBC, differential WCC, blood film.

Table 4 Reference intervals for leucocyte differential counts

Assessment of lymphocyte morphology assists in determining the aetiology of the lymphocytosis.

If lymphocytosis is persistent (>3 months) and the aetiology is uncertain, immunophenotyping may be useful.

Mononucleosis syndromes 

Syndromes characterised by lymphoid cells with atypical morphology (ie activated lymphocytes).

Other infections, especially 

  • Perussis
  • Viral infection

Characteristically lymphocytes are morphologically normal or show "reactive features".

Hyposplenism / splenic atrophy or absence.

Associated features of hyposplenism in the peripheral blood film (Howell-Jolly bodies, tareget cells, acanthocytes, thrombocytosis).

See Splenic atrophy/absence

Reactive, especially

  • Viral infection
  • Felty syndrome

Transient lymphocytosis associated with physiological stress

Lymphoproliferative disorders, especially

Blood film morphology may be suggestive. Immunophenotyping has a role in sub-typing the lymphoid lineage, confirmation of clonality in B cell disorders and may identify a characteristic immunophenotype in some lymphoproliferative disorders.


Barbara Bain, Blood Cell - A Practical Guide. Third Edition, Blackwell Publishing