From the Guidelines
The diagnostic blood tests for leukemia include a complete blood count (CBC) with differential, peripheral blood smear, and flow cytometry to confirm the presence of ≥5000 monoclonal B lymphocytes/µl and characterize the leukemia cells. These tests can detect abnormal white blood cell counts, unusual cell types, or immature blood cells that may indicate leukemia. The CBC may show elevated white blood cell counts, although some leukemias can present with normal or low counts. Anemia (low red blood cells) and thrombocytopenia (low platelets) are also common findings 1.
The leukemia cells found in the blood smear are characteristically small, mature lymphocytes with a narrow border of cytoplasm and a dense nucleus lacking discernible nucleoli and having partially aggregated chromatin. CLL cells co-express the CD5 antigen and B-cell surface antigens CD19, CD20, and CD23, with characteristically low levels of surface immunoglobulin, CD20, and CD79b compared to normal B cells 1.
Additional specialized blood tests, such as cytogenetic testing and molecular studies, can help classify the specific type of leukemia, which is crucial for determining appropriate treatment. These tests identify specific cell markers, chromosomal abnormalities, and genetic mutations associated with different leukemia types. Early detection through blood testing is important as symptoms of leukemia, like fatigue, frequent infections, and easy bruising, can be vague and attributed to other conditions.
Key diagnostic criteria for chronic lymphocytic leukemia (CLL) include:
- The presence of ≥5000 monoclonal B lymphocytes/µl in the peripheral blood for at least 3 months
- Confirmation of clonality by flow cytometry
- Characteristic morphology of leukemia cells on blood smear
- Co-expression of CD5 and B-cell surface antigens CD19, CD20, and CD23
- Restricted expression of either λ or κ immunoglobulin light chains 1.
From the Research
Diagnostic Blood Tests for Leukemia
The diagnosis of leukemia can be made based on various blood tests, including:
- Peripheral blood smear review to identify specimens for flow cytometric immunophenotyping 2
- Flow cytometry to characterize leukemias by immunotyping, which is particularly helpful when the morphology is difficult to interpret 3, 4
- Complete blood count (CBC) and differentials to screen for chronic myeloid leukemia (CML) 5
- Multiparametric flow cytometry to diagnose and classify acute leukemia 6, 4
Specific Markers and Tests
Some specific markers and tests used in the diagnosis of leukemia include:
- CD3, CD7, CD5 for T lymphocytes lineage 3
- CD19, CD22, CD20, CD10 for B lymphocytes lineage 3
- CD13, CD14, CD33 for myeloid subsets 3
- TDT, HLA-DR, CD45 for non-lineage restricted markers 3
- Neutrophil alkaline phosphatase (NAP) score to screen for CML 5
- Basophil and immature granulocyte counts to screen for CML 5
Comparison of Blood and Bone Marrow Tests
Studies have compared the results of blood and bone marrow tests in the diagnosis of leukemia, including:
- A study that found that peripheral blood smear review and flow cytometric immunophenotyping can be used to diagnose chronic lymphocytic leukemia without the need for bone marrow evaluation 2
- A study that found that flow cytometry can be used to diagnose acute leukemia using peripheral blood or bone marrow samples 3
- A study that found that bone marrow evaluation is still the de facto standard for response assessment in acute myeloid leukemia, but peripheral blood evaluation may be adequate for monitoring relapse 6