**Question:** A 9-year-old boy presents with fever, feeling unwell, and easy bruising on his legs. On examination he is pale, blood pressure 100/60 mm Hg, pulse 100/min, and temperature 37.8°C. His lungs are clear, abdomen is soft with a palpable spleen, and there are petechiae and bruises on his legs. His CBC reveals a hemoglobin of 8.5 g/dL, WBC of 17,000/mL, and platelets of 30,000/mL. A blood film reveals neutropenia and leukemic lymphoblasts. Which of the following is the most appropriate initial diagnostic test to confirm the diagnosis?

A. Complete blood count (CBC)
B. Splenomegaly
C. Blood film
D. Bone marrow aspiration and biopsy

**Correct Answer:**

**Core Concept:** Leukemia is a group of blood-related cancers that affect the bone marrow and blood cells. In this case, the patient presents with clinical manifestations like fever, easy bruising, and splenomegaly, along with abnormal white blood cell (WBC) count and presence of leukemic lymphoblasts on blood film.

**Why the Correct Answer is D:**

The correct answer is D, "Bone marrow aspiration and biopsy." The diagnosis of leukemia in this scenario is suggested by the following:

1. Abnormal WBC count: The patient has a WBC count of 17,000/mL, which is an extremely high level, indicating leukocytosis and suggesting leukemia.
2. Presence of leukemic lymphoblasts on blood film: A blood film reveals abnormal white blood cells, specifically leukemic lymphoblasts, which are immature forms of white blood cells commonly found in leukemia.

**Why Other Options Are Incorrect:**

A: A complete blood count (CBC) may be initially performed to confirm the suspicion of leukemia, but it is not the definitive test for diagnosis. A CBC alone may not reveal the presence of leukemic cells.

B: Splenomegaly is a common clinical finding in leukemia, but it is not a diagnostic test. Bone marrow aspiration and biopsy are required for a definitive diagnosis.

C: A blood film is essential for identifying the presence of leukemic cells, but it is not a definitive test for diagnosis. A complete blood count, blood film, and physical examination can suggest the diagnosis, but bone marrow aspiration and biopsy are required for a definitive diagnosis of leukemia.

D: Bone marrow aspiration and biopsy are the definitive tests for diagnosing leukemia, as they reveal the presence of leukemic cells in the bone marrow, confirming the suspected diagnosis.