What is the gold standard diagnostic procedure for leukemia?

• A. Bone marrow biopsy
• B. Complete blood count
• C. Peripheral blood smear
• D. Flow cytometry

Answer: (A)

Bone marrow examination is the definitive way to diagnose leukemia because it directly reveals whether malignant blasts are present in the marrow, their percentage, and their cell lineage. A bone marrow biopsy with aspirate provides essential information on cellularity, morphology, and architecture, and is required to confirm leukemia and to classify it according to WHO criteria. From this sample, cytogenetic and molecular studies can be performed, which are crucial for prognosis and guiding treatment.

A complete blood count can signal a problem and a peripheral smear may show circulating blasts, but neither alone confirms the diagnosis or substitutes for the marrow tissue. Flow cytometry is invaluable for identifying the leukemia subtype by immunophenotyping, but it relies on a marrow or blood sample and is not by itself the definitive diagnostic test. Thus, the marrow biopsy remains the gold standard.