A 32-year-old woman presents with fever, bleeding gums, and petechiae. CBC shows WBC 85,000/μL with 70% blasts, Hb 7.2 g/dL, and platelets 15,000/μL. Auer rods are seen on blood smear. Which investigation is most appropriate to confirm the diagnosis and guide treatment?

Question

Accepted Answer

A. Bone marrow aspiration and biopsy with cytochemical stains. ## Diagnosis of Acute Leukemia: Investigation Hierarchy

**Key Point:** Bone marrow aspiration and biopsy with cytochemical stains (MPO, PAS, Sudan Black) is the gold standard for morphologic diagnosis and classification of acute leukemias. While the blood smear may show blasts and Auer rods (highly suggestive of AML), bone marrow examination is mandatory for:
- Confirming >20% blasts in marrow (diagnostic threshold)
- Morphologic subtyping (FAB classification)
- Cytochemical differentiation of AML vs ALL
- Assessing cellularity and dysplasia

## Role of Each Investigation

| Investigation | Purpose | When Used |
|---|---|---|
| **Bone marrow aspiration & biopsy** | Morphology, cytochemistry, blast percentage | **Diagnostic gold standard** |
| Flow cytometry | Immunophenotyping, lineage assignment, prognostic markers | Confirmatory; essential for ALL and minimal residual disease |
| LDH, uric acid | Tumor burden, hyperuricemia risk | Prognostic; guides allopurinol/rasburicase |
| Imaging (CXR, USG) | Organomegaly, mediastinal mass | Staging; not diagnostic |

**High-Yield:** Auer rods on blood smear are pathognomonic for AML and strongly suggest the diagnosis, but bone marrow examination is still required to confirm blast percentage and classify the subtype (M0–M7).

**Clinical Pearl:** In this case, the presence of Auer rods + high WBC + blasts on blood smear makes acute leukemia virtually certain, but marrow biopsy remains the reference standard for formal diagnosis and is necessary before initiating chemotherapy.

## Why Bone Marrow Is Superior to Blood Smear Alone

1. **Quantification:** Blast percentage in marrow (not blood) defines leukemia (≥20% blasts)
2. **Cytochemistry:** MPO positivity confirms myeloid lineage; PAS pattern helps subtype
3. **Cellularity assessment:** Distinguishes hypercellular from hypocellular presentations
4. **Dysplasia evaluation:** Identifies dysplastic changes in non-blast populations

Answer

B. Chest X-ray and abdominal ultrasound

Answer

C. Flow cytometry with immunophenotyping

Answer

D. Serum lactate dehydrogenase and uric acid

A 32-year-old woman presents with fever, bleeding gums, and petechiae. CBC shows WBC 85,000/μL with 70% blasts, Hb 7.2 g/dL, and platelets 15,000/μL. Auer rods are seen on blood smear. Which investigation is most appropriate to confirm the diagnosis and guide treatment?

Explanation

Diagnosis of Acute Leukemia: Investigation Hierarchy

Role of Each Investigation

Why Bone Marrow Is Superior to Blood Smear Alone

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Investigation	Purpose	When Used
Bone marrow aspiration & biopsy	Morphology, cytochemistry, blast percentage	Diagnostic gold standard
Flow cytometry	Immunophenotyping, lineage assignment, prognostic markers	Confirmatory; essential for ALL and minimal residual disease
LDH, uric acid	Tumor burden, hyperuricemia risk	Prognostic; guides allopurinol/rasburicase
Imaging (CXR, USG)	Organomegaly, mediastinal mass	Staging; not diagnostic