Test

Background

Typical CLL can be diagnosed with some confidence using flow cytometry. However, atypical cases are regularly encoutered and can cause diagnosic difficulty.

This image shows a typical CLL cells and a dot plot of CD45/SSc. Note that although the CLL cells (shown in blue) generally lie close to the position of normal lymphocytes, consistent with their "anergic nature": CLL cells express low levels of B-cell receptor associated molecules (e.g. CD19, CD79B and sIg) and also will generally have lower expression of CD45 than typical T cells (shown in red) or NK cells (shown in green). CLL often has a wide range of CD45 expression causing the population to have a "sausage like" shape on a CD45/SSc plot.

file CLL image file CD45CLL.jpg left 250px

Immunophenotype of CLL
Major markers useful in CLL diagnosis
Light chains	Wk	Either weak resticted κ or λ or undetectable expression
CD19	Wk/mod	Expression is expected, but less strong than normal B cells
CD20	Wk	Expression is expected, but characteristically weak
CD79A	Wk	Expression is expected, but characteristically weak
FMC7	Wk	May be expressed by atypical cases, generally absent

Immunophenotype:

Markers of B-lineage

• Immunoglobulin light chains: expect either light chain restriction with low intensity, or undetectable expression
• CD19 should be detected, but intensity is generally weak in CLL
• CD20 has expected expression in CLL, but intensity is generally weak
• CD79b expression is characteristically weak in CLL

Markers allowing diagnostic distinction

• FMC7 will have low or absent expression, high expression is particularly may suggest alternative disorders such as MCL or MZL
• CD5 should be expressed at moderate intensity in CLL (note also on expressed on mcl and occasionally on other lpd)
• CD23 has expected expression in CLL often at low intensity, generally absent in mcl but variably present on other lpd
• CD200 expressed on most CLL cases as well as other b-lpd but is most frequently absent in mcl optional markers extended panel for atypical cases
• CD43 a pan b-cell marker with expected expression in CLL; frequently but not always absent in mcl

Pitfalls