## Diagnostic Approach to Childhood Leukemia ### Role of Bone Marrow Aspiration **Key Point:** Bone marrow aspiration with cytomorphologic examination is the gold standard and investigation of choice for confirming acute leukemia and determining morphologic subtype (FAB classification). **High-Yield:** The bone marrow aspirate allows: - Morphologic identification of blast type (L1, L2, L3 in ALL; M0–M7 in AML) - Assessment of blast percentage (>20% confirms acute leukemia) - Evaluation of cellularity and dysplasia - Cytochemical stains (MPO, PAS, Sudan black) to differentiate ALL from AML ### Why Bone Marrow Is First-Line Although peripheral blood in this case shows abundant blasts (60%), bone marrow aspiration remains the diagnostic standard because: 1. It provides morphologic detail and cytochemical confirmation 2. It establishes the FAB subtype, which guides treatment intensity 3. It allows assessment of marrow cellularity and dysplasia 4. Cytochemical stains (MPO positive in AML, PAS positive in ALL) are diagnostic ### Complementary Investigations | Investigation | Timing | Purpose | |---|---|---| | **Bone marrow aspiration + cytomorphology** | At diagnosis | Morphologic confirmation, FAB subtype | | **Flow cytometry** | At diagnosis (concurrent) | Immunophenotyping, prognosis, MRD monitoring | | **Cytogenetics + FISH** | At diagnosis | Prognostic stratification (e.g., t(9;22), t(12;21)) | | **Lumbar puncture (CNS prophylaxis assessment)** | After remission induction | Assess CNS involvement | **Clinical Pearl:** In modern practice, bone marrow aspiration is performed concurrently with flow cytometry and cytogenetics at diagnosis. However, morphology remains the gold standard for initial confirmation. **Mnemonic — FAB Subtypes of ALL:** **L1-L3** = Lymphoblastic (L1 most common in children, L3 is Burkitt-like). [cite:Park 26e Ch 12] 
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