What are the diagnostic criteria for acute leukemia?

Diagnostic Criteria for Acute Leukemia

The diagnosis of acute leukemia requires a comprehensive approach including bone marrow examination with morphologic evaluation, immunophenotyping, cytogenetic analysis, and molecular genetic testing, with at least 30% blast cells in the bone marrow aspirate being the primary diagnostic criterion. 1

Initial Diagnostic Workup

Required Specimens and Laboratory Tests

• Complete blood count (CBC) with peripheral blood (PB) differential count and smear review 1
• Bone marrow (BM) aspirate, touch imprint, cell clots, and core biopsy for morphologic examination 1
• If BM aspirate is unobtainable or results in a dry tap, perform cell count and review morphology on touch imprint preparation 1
• Comprehensive metabolism panel to monitor for potential tumor lysis syndrome at diagnosis and during treatment 1

Essential Diagnostic Tests

• Multicolor comprehensive flow cytometry on BM aspirate (or PB if BM unavailable) to determine lineage (B-ALL, T-ALL, AML, or MPAL) 1, 2
• Conventional karyotyping (must be performed on BM) 1
• Fluorescence in situ hybridization (FISH) according to the subclassification of acute leukemia 1
• Molecular studies (PCR, RT-PCR, NGS) selective based on the subtype of acute leukemia 1

Specific Criteria by Leukemia Type

Acute Myeloid Leukemia (AML)

• Morphologic examination showing ≥20% myeloblasts in BM or PB 3
• Myeloperoxidase (MPO) and nonspecific esterase (NSE) for diagnosis and subclassification 1, 4
• Rapid FISH for PML-RARA if acute promyelocytic leukemia (APL) is suspected 1
• Molecular testing for FLT3-ITD, IDH1, IDH2, TET2, WT1, DNMT3A, and/or TP53 for prognosis and targeted therapy 1
• Additional testing for CEBPA, RUNX1, KIT (when core-binding factor AML is diagnosed) 1
• DIC profile only if APL is suspected 1

Acute Lymphoblastic Leukemia (ALL)

• Morphologic examination showing ≥20% lymphoblasts in BM or PB 3
• FISH for t(9;22)(q34.1;q11.2)/BCR-ABL1 and KMT2A(MLL) gene translocation in adult ALL 1
• FISH for t(12;21)(p13.2;q22.1)/ETV6-RUNX1, iAMP21, Trisomy 4 and 10, t(9;22) in childhood ALL 1
• Molecular studies for PAX-5, JAK1, JAK2, and/or IKZF1 for B-ALL 1
• Molecular studies for NOTCH1 and/or FBXW7 for T-ALL 1

Mixed Phenotypic Acute Leukemia (MPAL)

• FISH for t(9;22)(q34.1;q11.2)/BCR-ABL1 1
• FISH for KMT2A(MLL) gene translocation 1
• Flow cytometry showing expression of both myeloid and lymphoid markers 2, 5

Extramedullary Acute Leukemia

• If PB or BM is positive, no additional biopsy of extramedullary tumor is necessary 1
• If no BM or PB involvement, tissue biopsy with morphologic examination, immunophenotyping, and cytogenetics is required 1

Cerebrospinal Fluid Evaluation

• Lumbar puncture with CSF cell count and cytology examination 1
• Flow cytometry on CSF 1
• IHC study with TdT stain for ALL 1

Important Considerations and Pitfalls

• Flow cytometric immunophenotyping and karyotype analysis have been implemented in most diagnostic laboratories (99% and 96%, respectively), while cytochemical studies are less common and mainly used when limited samples are available or flow cytometry results are ambiguous 1
• Detailed immunophenotypic profiles can be associated with specific molecular defects and well-defined biology 2, 5
• Genetic abnormalities are present in more than 80% of ALLs and more than 90% of AMLs, making cytogenetic and molecular analysis crucial for proper classification 5
• Proper specimen handling is critical - harvested specimens (fresh, frozen, or paraffin embedded) and their nucleic acid products should be properly identified and stored under appropriate conditions for additional diagnostic, prognostic, or therapeutic purposes 1, 3
• Sudan Black B, periodic acid-Schiff, or acid phosphatase are not recommended as routine tests for acute leukemia 1