**Core Concept**
In chronic renal failure, the kidneys' inability to effectively filter waste products leads to a buildup of uremic toxins, which can cause various changes in the blood, including alterations in red blood cell (RBC) morphology. The type of RBC seen in chronic renal failure is a result of the body's attempt to compensate for the lack of erythropoietin, a hormone produced by the kidneys that stimulates red blood cell production.

**Why the Correct Answer is Right**
In chronic renal failure, the decreased production of erythropoietin leads to a decrease in red blood cell production, resulting in anemia. However, some RBCs may be larger than normal, a condition known as **macrocytosis**. This is due to the compensatory increase in red blood cell production by the bone marrow, leading to the release of larger, more immature RBCs into the circulation. These larger RBCs are often seen in patients with chronic renal failure and are a result of the body's attempt to maintain adequate oxygen delivery to tissues despite the anemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because normocytic anemia is a more common finding in chronic renal failure, but it does not specifically describe the changes in RBC morphology seen in this condition.
* **Option B:** This is incorrect because spherocytosis is a condition characterized by the presence of sphere-shaped RBCs, which is not typically seen in chronic renal failure.
* **Option C:** This is incorrect because poikilocytosis is a condition characterized by the presence of abnormally shaped RBCs, which can be seen in various conditions, including hemolytic anemia, but is not specific to chronic renal failure.

**Clinical Pearl / High-Yield Fact**
In patients with chronic renal failure, the presence of macrocytosis can be a clue to the underlying diagnosis, and it is essential to consider this in the differential diagnosis of anemia in this population.

**Correct Answer:** C. Macrocytosis