**Core Concept**
Post-thyroid surgery, patients are at risk of developing hypocalcemia due to damage to the parathyroid glands, which are responsible for regulating calcium levels in the blood. The parathyroid glands secrete parathyroid hormone (PTH), which stimulates osteoclasts to break down bone tissue and release calcium ions into the bloodstream.

**Why the Correct Answer is Right**
The patient's blood calcium level of 8.9 meq is below the normal range, indicating hypocalcemia. Perioral tingling is a classic symptom of hypocalcemia. The next step is to administer calcium gluconate or calcium chloride to correct the hypocalcemia. This will help to alleviate the symptoms of hypocalcemia, such as tingling, and prevent more severe complications like tetany or seizures.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering vitamin D would not directly address the acute hypocalcemia in this patient. While vitamin D is essential for calcium absorption in the gut, it would not provide an immediate correction of the low calcium levels.

**Option B:** Ordering a repeat calcium level would not address the patient's current hypocalcemia and perioral tingling. The priority is to correct the low calcium levels, not to confirm the diagnosis.

**Option C:** Administering calcitonin would actually worsen the patient's hypocalcemia. Calcitonin is a hormone that lowers blood calcium levels by inhibiting osteoclast activity and promoting calcium excretion by the kidneys.

**Clinical Pearl / High-Yield Fact**
After thyroid surgery, patients with hypocalcemia should be monitored closely for signs of tetany, such as muscle cramps, spasms, or seizures. Early recognition and treatment of hypocalcemia can prevent these complications.

**Correct Answer: C. Administering calcitonin would actually worsen the patient's hypocalcemia.**