In a 6-year-old boy with recent upper respiratory infection, pallor, ecchymoses, petechiae, thrombocytopenia and anemia with a normal white blood cell count, which investigation is most appropriate to confirm the diagnosis: coagulation factor studies, bone‑marrow biopsy, or Epstein–Barr virus serology?

Bone Marrow Biopsy is the Most Appropriate Investigation

In a 6-year-old with pancytopenia (thrombocytopenia and anemia), petechiae, ecchymoses, and a recent upper respiratory infection, bone marrow biopsy is the most appropriate investigation to confirm the diagnosis and exclude acute leukemia or other bone marrow pathology.

Clinical Reasoning

The key diagnostic concern here is distinguishing between benign post-viral thrombocytopenia (such as immune thrombocytopenic purpura) and a malignant bone marrow process:

• The combination of low platelets AND low hemoglobin with normal WBC is atypical for isolated ITP, which typically presents with isolated thrombocytopenia and otherwise normal blood counts 1, 2

• Bicytopenia (thrombocytopenia + anemia) raises concern for bone marrow infiltration or failure, particularly acute lymphoblastic leukemia (ALL), which is the most common childhood malignancy and can present with cytopenias, bruising, and petechiae following a viral prodrome 3, 4

• Post-viral ITP would be expected to show isolated thrombocytopenia with normal hemoglobin and WBC, not the bicytopenia pattern described here 1, 2

Why Not the Other Options

Coagulation Factors (Option A)

• Coagulation factor studies are not indicated because the clinical presentation (petechiae, ecchymoses, thrombocytopenia) is consistent with a platelet disorder, not a coagulation factor deficiency 5, 3
• Coagulation disorders typically present with deep tissue bleeding (hemarthroses, muscle hematomas) rather than superficial petechiae and ecchymoses 5

EBV Serology (Option C)

• While EBV can trigger ITP or be associated with hemophagocytic lymphohistiocytosis, EBV serology does not confirm the underlying hematologic diagnosis causing the bicytopenia 5
• EBV testing would be supplementary, not diagnostic for the primary bone marrow pathology that must be excluded 5, 6
• The presence of bicytopenia necessitates bone marrow evaluation regardless of EBV status 5

Critical Pitfalls to Avoid

Never assume post-viral ITP in a child with multiple cytopenias without bone marrow examination - this is the most dangerous diagnostic error, as it may delay diagnosis of acute leukemia 2, 3

The normal WBC count does not exclude leukemia, as ALL can present with normal, low, or elevated WBC counts depending on the stage and subtype 4