Diagnosis of Acute Promyelocytic Leukemia (APL)

Initial Clinical Recognition

• Suspect APL in any patient presenting with characteristic morphology showing abnormal promyelocytes with heavy granulation or bilobed nuclei with minimal granulation 3
• Suspect APL in patients with severe coagulopathy or disseminated intravascular coagulation (DIC), particularly in the setting of acute leukemia 1, 4, 5
• Immunophenotype showing CD34-negative, HLA-DR-negative/dim blasts with strong CD13/CD33 positivity and abnormally low CD15 expression is suggestive of APL 3

Mandatory Diagnostic Workup

• Obtain bone marrow aspirate as the preferred specimen for all diagnostic studies; peripheral blood may be used only if bone marrow is unobtainable or contraindicated, or when blast count is sufficiently high 1, 6, 3
• Perform Romanowsky-derived stains on bone marrow aspirate smears 3
• Conduct myeloperoxidase (MPO) or Sudan Black B staining for diagnosis and subclassification 1, 4, 3
• Evaluate peripheral blood smear and complete blood count with differential 7
• Rapid FISH for PML-RARA detection on bone marrow is the critical first-line genetic test when APL is suspected, as it provides results within 24-48 hours 1, 4, 6
• Molecular confirmation by RT-PCR for PML-RARA fusion transcripts is mandatory for definitive diagnosis and must be performed on bone marrow or peripheral blood samples 1, 4, 2, 3
• Conventional karyotyping should be performed to identify t(15;17)(q22;q21) translocation, though this is time-consuming and may miss cryptic rearrangements 3

Immunophenotyping and Coagulation Studies

• Perform multiparameter flow cytometry to increase diagnostic accuracy, particularly for microgranular variants 1, 8, 3
• Obtain DIC profile immediately when APL is suspected, including PT, PTT, fibrinogen, D-dimer, and platelet count 1, 4, 8, 5
• Coagulation screening must be performed before central line insertion 5

Additional Molecular Testing for Risk Stratification

• Test for FLT3-ITD mutation in all confirmed APL cases for prognostic purposes 1, 4, 9

Critical Considerations

• The American Society of Clinical Oncology recommends starting ATRA therapy before genetic confirmation and performing rapid FISH for PML-RARA on bone marrow samples when APL is suspected based on morphology or clinical presentation 1, 2, 3
• Discontinue ATRA if t(15;17) translocation or PML-RARA fusion is not confirmed 2