What are the diagnostic tests for Acute Myeloid Leukemia (AML)?

Diagnostic Tests for Acute Myeloid Leukemia (AML)

The comprehensive diagnostic workup for AML requires bone marrow examination with aspirate and biopsy, along with peripheral blood evaluation, supported by flow cytometry, cytogenetic analysis, and molecular genetic testing to establish diagnosis, classify disease subtype, and determine prognosis. 1

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential

  • Essential first step showing cytopenias and/or leukocytosis
  • Peripheral blood smear review for blast identification 1

• Comprehensive metabolic panel

  • Assess for tumor lysis syndrome (uric acid, phosphate, LDH)
  • Evaluate liver and kidney function 1

• Coagulation studies

  • Prothrombin time, partial thromboplastin time, fibrinogen
  • Critical for detecting early disseminated intravascular coagulation, especially in acute promyelocytic leukemia 1

Core Diagnostic Tests

1. Bone Marrow Examination

• Bone marrow aspirate

  • Required for morphologic evaluation of blasts
  • Minimum 500 nucleated cells should be counted
  • ≥20% blasts required for AML diagnosis (with exceptions) 1
  • If dry tap occurs, touch preparations from core biopsy should be evaluated 1

• Bone marrow trephine biopsy

  • Evaluates cellularity and architecture
  • Essential when aspirate is inadequate (dry tap)
  • Allows assessment of fibrosis 1

2. Immunophenotyping

• Multiparameter flow cytometry

  • Essential for lineage determination and subclassification
  • Myeloid markers: CD13, CD33, CD117, MPO, CD15, CD65 1
  • Distinguishes AML from ALL and mixed phenotype acute leukemia
  • Should be performed on bone marrow aspirate or peripheral blood if sufficient blasts are present 1

• Immunohistochemistry

  • Alternative when flow cytometry not available
  • Used for core biopsies when aspirate inadequate 1

3. Genetic Studies

• Conventional cytogenetic analysis (karyotyping)

  • Mandatory component of AML evaluation
  • Detects chromosomal abnormalities with prognostic significance 1

• Fluorescence in situ hybridization (FISH)

  • Higher resolution than conventional cytogenetics
  • Rapid turnaround time for critical abnormalities
  • Particularly useful for detecting PML-RARA in suspected acute promyelocytic leukemia 1, 2

• Molecular genetic testing

  • Essential for risk stratification and treatment decisions
  • Key mutations to test:
    • FLT3-ITD
    • NPM1
    • CEBPA
    • IDH1/IDH2
    • RUNX1
    • TP53
    • TET2 1
  • Next-generation sequencing (NGS) panels increasingly used 3

Supplementary Tests

1. Cytochemistry

• Myeloperoxidase (MPO) and nonspecific esterase (NSE)
  • Less commonly used now (only 24.8% of labs)
  • Useful when flow cytometry unavailable or results ambiguous
  • MPO positivity (≥3% of blasts) indicates myeloid differentiation 1

2. Cerebrospinal Fluid (CSF) Analysis

• Not routinely required for all AML patients
• Indicated for patients:
  • Receiving intrathecal therapy
  • With neurological symptoms
  • Without clinical contraindications 1
• Should include cell count, cytospin examination, and flow cytometry 1

3. Extramedullary Disease Assessment

• Tissue biopsy for extramedullary manifestations without bone marrow involvement
• Imaging studies to evaluate for mediastinal masses, organomegaly, or other tissue lesions 1

Practical Considerations

• If bone marrow aspiration is contraindicated or unsuccessful, diagnosis can be made from peripheral blood if sufficient blasts are present 1
• Specimens should be properly stored for future molecular testing 1
• Testing patterns vary between academic and community centers, with molecular testing more common in academic settings 4
• Recent guidelines emphasize the importance of comprehensive molecular profiling, with increasing adoption since 2016 4

Common Pitfalls to Avoid

1. Incomplete genetic testing - Missing critical mutations can lead to suboptimal treatment selection
2. Delayed testing for acute promyelocytic leukemia - Rapid FISH for PML-RARA is essential when APL is suspected due to risk of coagulopathy
3. Inadequate specimen collection - Ensure sufficient material for all required tests
4. Failure to integrate clinical history - Prior myelodysplastic syndrome or therapy-related exposure is critical for proper classification 5
5. Relying solely on peripheral blood when bone marrow examination is feasible

The diagnostic approach to AML has evolved significantly with advances in molecular diagnostics, making comprehensive genetic profiling increasingly important for accurate diagnosis, risk stratification, and treatment selection 6.