What laboratory tests are used to diagnose leukemia?

Laboratory Tests for Diagnosing Leukemia

The diagnosis of leukemia requires a comprehensive laboratory workup including complete blood count with differential, bone marrow aspiration and biopsy with morphologic examination, flow cytometry, cytogenetic analysis, and molecular genetic testing. 1

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential and peripheral blood smear review:

  • Essential first step to identify cytopenias, presence of abnormal cells/blasts, and establish baseline hematologic parameters
  • May show leukocytosis, anemia, thrombocytopenia, or pancytopenia
  • Peripheral blood smear examination can reveal presence of blast cells

• Blood Chemistry Profile:

  • Comprehensive metabolic panel
  • Liver function tests
  • Lactate dehydrogenase (LDH) - elevated levels associated with lymphoproliferative disorders
  • Tumor lysis syndrome panel
  • Disseminated intravascular coagulation (DIC) panel (particularly if acute promyelocytic leukemia is suspected) 1

Bone Marrow Evaluation

• Bone marrow aspiration and biopsy:
  • Diagnostic standard - confirms leukemia when ≥30% blast cells are present
  • Essential components include:
    • Morphologic examination of aspirate, touch imprint, and core biopsy
    • Cytochemical studies (if flow cytometry unavailable)
    • Immunophenotyping by flow cytometry
    • Cytogenetic analysis
    • Molecular genetic testing 1, 2

Specialized Testing

Immunophenotyping

• Flow cytometry:
  • Differentiates between myeloid and lymphoid lineages
  • Identifies specific leukemia subtypes
  • Detects minimal residual disease
  • Implemented in 99% of diagnostic laboratories in the US 1

Cytochemical Studies

• For AML diagnosis and subclassification:
  • Myeloperoxidase (MPO)
  • Nonspecific esterase (NSE)
  • Note: Less commonly used now (only 24.8% for AML and 14.2% for ALL) as they've been largely replaced by flow cytometry 1

Genetic Studies

• Cytogenetic analysis:

  • Karyotyping of G-banded metaphase chromosomes
  • Critical for prognostic stratification
  • Implemented in 96% of diagnostic laboratories in the US 1

• Fluorescence in situ hybridization (FISH):

  • For rapid detection of specific genetic abnormalities:
    • t(9;22)(q34.1;q11.2)/BCR-ABL1 in ALL and mixed phenotypic acute leukemia
    • PML-RARA if acute promyelocytic leukemia is suspected
    • KMT2A(MLL) gene translocations
    • ETV6-RUNX1, iAMP21, Trisomy 4 and 10 in childhood ALL 1

• Molecular genetic testing:

  • For AML: FLT3-ITD, IDH1, IDH2, TET2, WT1, DNMT3A, TP53, CEBPA, RUNX1, KIT, NPM1
  • For ALL: PAX-5, JAK1, JAK2, IKZF1, CRLF2, NOTCH1, FBXW7
  • Next-generation sequencing (NGS) for comprehensive mutation profiling 1

Cerebrospinal Fluid Analysis

• Lumbar puncture with CSF examination:
  • Indicated in ALL and high-risk AML
  • Components include:
    • Cell count
    • Cytospin examination
    • Flow cytometry
    • Enumeration of blasts 1

Type-Specific Laboratory Evaluation

Acute Myeloid Leukemia (AML)

• Cytochemical studies (MPO and NSE)
• Rapid FISH for PML-RARA if APL suspected
• Molecular genetic testing for FLT3-ITD, IDH1/2, TP53, etc.
• DIC profile if acute promyelocytic leukemia suspected 1

Acute Lymphoblastic Leukemia (ALL)

• FISH for t(9;22)/BCR-ABL1, KMT2A gene translocation
• Molecular studies for lineage-specific markers
• Immunoglobulin/TCR gene rearrangement studies 1

Mixed Phenotypic Acute Leukemia (MPAL)

• FISH for t(9;22)/BCR-ABL1, KMT2A gene translocation
• Comprehensive immunophenotyping 1

Extramedullary Leukemia

• Tissue biopsy with:
  • Morphologic examination
  • Immunohistochemistry
  • Fresh tissue for flow cytometry
  • Cytogenetics (karyotyping or FISH)
  • Molecular studies 1

Common Pitfalls and Caveats

• Inadequate bone marrow specimens may lead to misdiagnosis - ensure adequate sampling
• Delay in processing specimens can affect flow cytometry results
• Prior administration of chemotherapy or growth factors can alter morphologic findings
• Cytochemical studies are less reliable in cases with low blast percentages
• Some genetic abnormalities may be missed by conventional cytogenetics and require FISH or molecular testing 1, 3

Remember that the diagnosis of acute leukemia requires integration of clinical information with laboratory findings, and treatment decisions should be based on accurate classification of leukemia type and risk stratification 4, 3.