**Core Concept**
Contrast-induced acute kidney injury (CI-AKI) is a preventable cause of acute kidney injury, often occurring after the administration of iodinated contrast media used in radiographic procedures. It is characterized by a decline in kidney function, typically manifested by an increase in serum creatinine levels.

**Why the Correct Answer is Right**
The correct answer, **C. Dialysis requirement is usually uncommon**, reflects the generally favorable prognosis of CI-AKI. This is because most cases of CI-AKI are mild to moderate, with only a small percentage of patients requiring renal replacement therapy, such as dialysis. The kidneys' ability to recover from the insult caused by the contrast media is largely dependent on the pre-existing renal function and the presence of comorbid conditions. In most cases, supportive care, hydration, and monitoring are sufficient to manage CI-AKI, making dialysis requirement an uncommon occurrence.

**Why Each Wrong Option is Incorrect**
**Option A:** A rise in serum creatinine after 12 hours is not a definitive indicator of CI-AKI, as it can occur due to various other causes of acute kidney injury. The timing and magnitude of the rise in serum creatinine are crucial in diagnosing CI-AKI.

**Option B:** The peak in serum creatinine in CI-AKI typically occurs within 3-5 days after contrast exposure, not 2 weeks. This is because the kidneys' ability to recover from the insult caused by the contrast media is largely dependent on the pre-existing renal function.

**Option D:** High fractional excretion of sodium (FeNa) is not a common finding in CI-AKI. In fact, FeNa is often low or in the normal range in patients with CI-AKI, as the kidneys are unable to adequately reabsorb sodium due to the insult caused by the contrast media.

**Clinical Pearl / High-Yield Fact**
It is essential to note that patients with pre-existing renal impairment, diabetes, and heart failure are at a higher risk of developing CI-AKI. Preventive measures, such as adequate hydration and the use of contrast media with lower osmolarity, can significantly reduce the risk of CI-AKI.

**✓ Correct Answer: C. Dialysis requirement is usually uncommon**