**Core Concept**
Microcytic anemia is characterized by a reduced mean corpuscular volume (MCV) of red blood cells, typically less than 80 fL. This condition can be caused by various factors, including iron deficiency, thalassemia, or anemia of chronic disease.

**Why the Correct Answer is Right**
In this case, the patient's ferritin level is elevated at 100 g/L, which suggests iron overload rather than iron deficiency. However, the ferritin level is often used as a marker of iron stores, but it can also be elevated in acute phase reactions and inflammation. The patient's Hb level is low at 10 g/dL, indicating anemia. The combination of microcytic anemia and elevated ferritin points towards anemia of chronic disease (ACD), which is commonly seen in patients with chronic infections, inflammation, or malignancy.

In ACD, the body's iron stores are adequate, but the iron is not available for erythropoiesis due to the inflammatory response. This results in a decrease in the production of transferrin, the primary iron-transport protein, and an increase in the production of hepcidin, a hormone that inhibits iron release from macrophages.

**Why Each Wrong Option is Incorrect**

* **Option A:** Iron deficiency anemia is unlikely in this case, as the ferritin level is elevated, indicating adequate iron stores.
* **Option B:** Thalassemia major would typically present with more severe anemia and other characteristic features such as splenomegaly and marked microcytosis.
* **Option D:** Sideroblastic anemia is characterized by ringed sideroblasts in the bone marrow and is often associated with myelodysplastic syndromes or other myeloid malignancies.

**Clinical Pearl / High-Yield Fact**
Anemia of chronic disease is often misdiagnosed as iron deficiency anemia, leading to unnecessary iron supplementation. It is essential to consider the patient's clinical context, including the presence of chronic infections or inflammation, when evaluating microcytic anemia.

**Correct Answer: C. Anemia of chronic disease**