**Core Concept**
Hypochromic microcytic anemia is characterized by small, pale red blood cells with reduced hemoglobin content, often due to iron deficiency or thalassemia. This condition is commonly seen in patients with chronic blood loss, such as those requiring frequent blood transfusions.

**Why the Correct Answer is Right**
In this patient, the presence of hypochromic microcytic anemia and a history of frequent blood transfusions suggests iron deficiency anemia. The low MCV (60 fl) and low MCHC (not given) further support this diagnosis. Since the patient is already showing signs of iron deficiency, further investigation into iron metabolism is not necessary.

**Why Each Wrong Option is Incorrect**
* **Option A:** Serum iron levels would be useful in confirming the diagnosis of iron deficiency anemia, but in this case, the clinical presentation and history already point to iron deficiency.
* **Option B:** Total iron-binding capacity (TIBC) is an important test in diagnosing iron deficiency anemia, as it helps differentiate between iron deficiency and other causes of anemia. However, in this case, the clinical picture is already suggestive of iron deficiency.
* **Option C:** Ferritin levels are a more direct indicator of iron stores and would be useful in confirming the diagnosis of iron deficiency anemia. However, given the patient's history and clinical presentation, ferritin levels are likely to be low.
* **Option D:** Bone marrow examination is not necessary in this case, as the clinical presentation and laboratory findings are consistent with iron deficiency anemia.

**Clinical Pearl / High-Yield Fact**
In patients with chronic blood loss, iron deficiency anemia is often seen due to the body's inability to keep up with the demand for iron. Regular monitoring of hemoglobin and ferritin levels is essential to prevent severe anemia.

**Correct Answer:** D. Bone marrow examination.