What blood test can be done to screen for different kinds of leukemia?

Blood Tests for Screening Different Types of Leukemia

The complete blood count (CBC) with differential is the most essential initial blood test for screening various types of leukemia, as it can detect abnormalities in all blood cell lines and identify the presence of abnormal cells. 1

Initial Diagnostic Blood Tests

Complete Blood Count (CBC) with Differential

• Evaluates all three major cell lines: red blood cells, white blood cells, and platelets
• Can detect cytopenias (low blood counts) or elevated counts
• Differential count identifies abnormal cell populations, including:
  • Presence of blast cells (immature cells)
  • Abnormal lymphocyte morphology
  • Circulating immature cells
  • Abnormal white blood cell ratios

Peripheral Blood Smear Review

• Essential companion to CBC
• Allows morphologic assessment of blood cells
• Can identify characteristic cell features specific to different leukemia types:
  • Hairy cell projections in hairy cell leukemia
  • Small mature lymphocytes with dense nuclei in chronic lymphocytic leukemia
  • Immature blast cells in acute leukemias 2, 1

Additional Blood Tests Based on Initial Findings

For Suspected Myeloid Leukemias

• Lactate dehydrogenase (LDH) - typically elevated in leukemias
• Uric acid - may be elevated due to increased cell turnover
• Prothrombin time (PT) and partial thromboplastin time (PTT) - to assess coagulation status
• Fibrinogen - may be abnormal in acute leukemias
• Basophil count - elevated basophils (>0.43 × 10^9/L) are highly sensitive for chronic myeloid leukemia 3
• Neutrophil alkaline phosphatase (NAP) score - typically low in chronic myeloid leukemia 1

For Suspected Lymphoid Leukemias

• Immunophenotyping by flow cytometry - identifies specific cell surface markers:
  • For chronic lymphocytic leukemia: CD5, CD19, CD20, CD23 positivity 2
  • For hairy cell leukemia: CD19, CD20, CD11c, CD25, CD103, CD123, CD200 positivity 2

Confirmatory Testing (Following Abnormal Blood Tests)

Molecular and Cytogenetic Testing

• FISH (Fluorescence In Situ Hybridization) - detects specific chromosomal abnormalities:

  • BCR-ABL1 fusion for chronic myeloid leukemia
  • Other recurrent genetic abnormalities in acute leukemias 2, 1

• RT-PCR (Reverse Transcription Polymerase Chain Reaction) - for molecular diagnosis:

  • BCR-ABL1 fusion in chronic myeloid leukemia
  • Other specific gene rearrangements 2

Bone Marrow Examination

• While not strictly a blood test, this is typically the next step after abnormal blood findings
• Includes:
  • Bone marrow aspiration and biopsy
  • Cytogenetic analysis
  • Molecular testing
  • Immunophenotyping 2, 1

Leukemia-Specific Screening Approaches

Acute Myeloid Leukemia (AML)

• CBC with differential showing cytopenias and/or presence of blasts
• Bone marrow examination with cytogenetics and molecular testing for mutations (KIT, FLT3-ITD, NPM1, CEBPA) 2

Chronic Myeloid Leukemia (CML)

• CBC with differential showing leukocytosis, often with basophilia
• Peripheral blood can be used for BCR-ABL1 testing by FISH or RT-PCR 2, 4

Chronic Lymphocytic Leukemia (CLL)

• CBC with differential showing lymphocytosis (≥5000 monoclonal B lymphocytes/µl)
• Flow cytometry confirming CD5, CD19, CD20, CD23 positivity with light chain restriction 2

Hairy Cell Leukemia

• CBC with differential showing pancytopenia
• Flow cytometry showing characteristic immunophenotype (CD19, CD20, CD11c, CD25, CD103, CD123, CD200) 2

Important Caveats and Pitfalls

• CBC alone is not diagnostic but serves as an initial screening test 5
• False negatives can occur in early-stage disease or with aleukemic presentations
• Some leukemias may present with normal white blood cell counts but abnormal cell morphology
• Reactive conditions can sometimes mimic leukemia on CBC, requiring expert interpretation
• Definitive diagnosis typically requires bone marrow examination with specialized testing
• Timing of testing is important - some treatments can temporarily normalize blood counts

Remember that while blood tests are crucial for screening and diagnosis, they should be interpreted in the context of the patient's clinical presentation and followed by appropriate confirmatory testing.