After total thyroidectomy, which hormone is required for lifelong replacement therapy?

• A. Insulin
• B. Calcitonin
• C. Parathyroid hormone
• D. Levothyroxine

Answer: (D)

When the thyroid gland is removed, the body can no longer produce thyroid hormones (T4 and T3), which regulate metabolism. To prevent hypothyroidism, lifelong replacement with a synthetic thyroid hormone is required. The standard choice is levothyroxine, a synthetic form of thyroxine (T4) that the body converts to the active T3 as needed. Dosing is individualized and guided by thyroid-stimulating hormone (TSH) levels to keep metabolism normal. Other options listed aren’t used for thyroid hormone replacement: insulin treats diabetes, while calcitonin and parathyroid hormone are involved in calcium regulation and aren’t required lifelong replacements after thyroidectomy. If the parathyroids were affected during surgery, calcium management may be needed, but that’s separate from thyroid hormone replacement.