Diagnosis

A definitive diagnosis of CLL is achieved through a combination of a lymphocytosis and characteristic lymphocyte morphology and immunophenotype (1).

Although a lymphocyte count of >5 x 10^9/l is classically considered to be the arbitrary threshold for the diagnosis of CLL, the diagnosis relies on the presence of a chronic, absolute increase in blood lymphocytes together with morphologic and immunophenotypic characteristics (2)

The International Workshop on Chronic Lymphocytic Leukaemia (IWCLL) proposed the following criteria for the diagnosis of CLL (based on modified criteria proposed originally by the National Cancer Institute):

• peripheral blood lymphocytes (x 109/l) -
  • not specified (a lower value than 5 × 10^9/L, is acceptable provided there is chronic, absolute increase in blood lymphocytes with the characteristic morphology and immunophenotype)
    
    
• morphology -
  • small mature lymphocytes without visible nucleoli
  • smudge cells
    
    
• immunophenotype of lymphocytes
  • >=1 B cell marker (CD19, CD 20 or CD 23) and CD 5 positivity in the absence of other pan-T-cell marker
  • monoclonal expression of either kappa or lambda immunoglobulin light chains
  • low density surface Ig
    
    
• atypical cells (e.g. - prolymphocytes)
  • <55% and/or <15 x 109/l
    
    
• duration of lymphocytosis
  • not specified but needs to be chronic
    
    
• bone marrow lymphocytes (%)
  • bone marrow evaluation not required (bone marrow evaluation is no longer required for the diagnosis but useful to determine extent and pattern of involvement and clarification of etiology of cytopaenias)

Reference:

• 1. Yee KW, O'Brien SM. Chronic lymphocytic leukemia: diagnosis and treatment. Mayo Clin Proc. 2006;81(8):1105-29.
• 2. Binet JL et al. Perspectives on the use of new diagnostic tools in the treatment of chronic lymphocytic leukemia. Blood. 2006;107(3):859-61