How is acute myeloid leukemia diagnosed?

Diagnosis of Acute Myeloid Leukemia

The diagnosis of AML requires peripheral blood and/or bone marrow evaluation with cytomorphology showing ≥20% blasts, combined with multicolor flow cytometry immunophenotyping, cytogenetic analysis (karyotyping and/or FISH), and molecular testing using gene panels or next-generation sequencing to establish the diagnosis and guide risk stratification 1, 2, 3.

Initial Clinical and Laboratory Assessment

When AML is suspected, immediately obtain:

• Complete blood count with manual differential - look for circulating blasts, cytopenias (anemia, thrombocytopenia, neutropenia) 1
• Comprehensive metabolic panel, lactate dehydrogenase, phosphate, and uric acid - essential for detecting tumor lysis syndrome, particularly important before initiating therapy 1
• Coagulation panel (PT, PTT, fibrinogen) - critical to detect early disseminated intravascular coagulation, especially in acute promyelocytic leukemia 1
• Document ethnicity/race - Hispanics have worse outcomes in acute leukemia and higher incidence of certain molecular subtypes 1
• Environmental/occupational exposure history - benzene, formaldehyde, butadiene, ionizing radiation 1

Diagnostic Specimen Collection Algorithm

If peripheral blood shows sufficient blasts (typically >5-10%), perform the complete diagnostic panel on peripheral blood first - this includes manual differential, flow cytometry, FISH, and molecular testing 1. This approach is critical when:

• The patient is clinically unstable and cannot tolerate bone marrow biopsy
• You need rapid diagnosis to initiate therapy
• There is concern about a dry tap

Bone marrow aspiration and biopsy remain the gold standard and should include 1, 3:

• Morphologic examination of aspirate, touch imprints, cell clots, and core biopsy
• If dry tap occurs, perform cell count and morphology review on touch imprint preparations
• Core biopsy provides architecture assessment and backup material for immunohistochemistry

Required Diagnostic Studies

1. Flow Cytometry Immunophenotyping

• Multicolor comprehensive panel covering B-ALL, T-ALL, AML, and mixed phenotype acute leukemia (MPAL) 1, 4
• Perform on bone marrow aspirate; if unavailable, use peripheral blood or core biopsy tissue
• Do not repeat flow cytometry on bone marrow if already diagnostic on peripheral blood - this avoids unnecessary testing 1

2. Cytogenetic Analysis

• Conventional karyotyping - identifies chromosomal abnormalities critical for risk stratification 2, 3
• FISH panels - detects specific recurrent abnormalities when karyotype fails or for rapid results 1, 3

3. Molecular Testing

• Next-generation sequencing gene panels - mandatory for detecting mutations in FLT3, NPM1, CEBPA, IDH1, IDH2, TP53, RUNX1, ASXL1, and others 2, 3
• These mutations determine eligibility for targeted therapies (FLT3 inhibitors, IDH inhibitors, venetoclax combinations) and refine risk stratification per ELN 2022 criteria 2
• Consider germline testing if family history suggests inherited predisposition (young age, family history of myeloid neoplasms, specific mutation patterns) 5, 3

Imaging Studies

Obtain imaging to assess:

• Chest radiograph or CT - evaluate for mediastinal masses, pulmonary infiltrates
• Abdominal imaging - assess hepatosplenomegaly, lymphadenopathy
• Document any extramedullary disease - skin, CNS, soft tissue masses 1

Critical Pitfalls to Avoid

Do not perform extramedullary tissue biopsy if complete ancillary studies have been completed on peripheral blood or bone marrow - repeat biopsy is only necessary when blood and marrow are uninvolved 1.

Do not delay molecular testing - FLT3-ITD status must be known within 48-72 hours as it determines whether to add midostaurin or other FLT3 inhibitors to induction therapy 2.

Do not miss acute promyelocytic leukemia (APL) - if morphology suggests APL (promyelocytes with Auer rods, abnormal granulation), immediately send PML-RARA testing and consider empiric all-trans retinoic acid (ATRA) therapy before confirmation, as APL is a medical emergency due to DIC risk 1.

Integration for Final Diagnosis

The diagnosis requires integration of 2, 3:

1. Blast percentage ≥20% in blood or marrow (lower thresholds apply for AML with specific genetic abnormalities per WHO-HAEM5 and ICC classifications)
2. Immunophenotype confirming myeloid lineage
3. Cytogenetic and molecular profile for WHO/ICC subclassification
4. Risk stratification using ELN 2022 criteria based on cytogenetics and molecular findings

This integrated approach enables precise diagnosis, identifies therapeutic targets (FLT3, IDH1/2, CD33), and establishes baseline for measurable residual disease monitoring 4, 2.