**Core Concept**
The underlying principle being tested is the diagnosis of microcytic hypochromic anemia, characterized by small (microcytic) and pale (hypochromic) red blood cells. This condition can be caused by various factors, including iron deficiency, thalassemia, and anemia of chronic disease. The key to diagnosis lies in interpreting laboratory values such as serum iron, ferritin, and transferrin saturation.

**Why the Correct Answer is Right**
Given the patient's serum iron is 20 μg/dl, ferritin level is 800 ng/ml, and transferrin percentage saturation is 64%, these values suggest iron overload rather than deficiency. The high ferritin level, in particular, indicates an excess of iron storage, which can be seen in conditions like hemochromatosis or transfusional iron overload. The microcytic hypochromic anemia in this context could be due to a condition that leads to ineffective erythropoiesis or iron sequestration, despite adequate iron stores.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested a diagnosis not consistent with iron overload and microcytic hypochromic anemia.
**Option B:** Similarly, would be incorrect if it implied a condition that does not align with the laboratory findings of high ferritin and transferrin saturation.
**Option C:** Incorrect if it represents a diagnosis that is not compatible with the patient's iron studies and anemia type.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that a high ferritin level, as seen in this patient, can indicate iron overload but also can be elevated in inflammatory conditions. Thus, interpreting ferritin levels requires consideration of the clinical context, including other markers of inflammation and iron status.

**Correct Answer:** D. Anemia of Chronic Disease