Diagnosis of leukaemias – conventional techniques
An abnormal complete blood count (CBC) raises the suspicion of acute myeloid/lymphoblastic leukaemia (AML/ALL), chronic myeloid leukaemia (CML) or myelodysplastic syndrome (MDS).
In leukaemia patients, white blood cell counts can be either elevated or depleted.
Bone marrow aspirate and histology are mandatory to establish the diagnosis.
Cytomorphology is a rapid but observer-dependent technique that allows the diagnosis of most AML and MDS cases.
Morphology is used to quantify blasts in peripheral blood and bone marrow, where ≥20% is the World Health Organization (WHO) cut off to diagnose acute leukaemia.
Cytochemistry is used to subspecify cells and to assess the iron storage, which is especially helpful in discriminating MDS subtypes.
Flow cytometry using fluorochrome antibody conjugates identifies blast cells and is a valuable tool to differentiate AML from ALL.
Typically, AML blasts have low side scatter (SSlow), show low expression of CD45 (CD45low), express CD34, CD13, CD117, CD133, MPO (myeloperoxidase) and can have aberrant expression of CD2, CD5, CD7, CD56, CD11b and CD15.
The leukaemia-associated (aberrant) immunophenotype (LAIP) is a valuable tool to detect minimal residual disease (MRD) following treatment.
Revision Questions
- What is the first diagnostic test used for leukaemia or MDS?
- Does a white blood cell count of 1000/μL rule out leukaemia?
- What is the main indication for flow cytometry in leukaemia diagnosis?
