A nurse is caring for a client who has a prescription for levothyroxine. Which of the following laboratory tests should the nurse monitor?

Levothyroxine is a medication used to treat hypothyroidism, and monitoring the TSH levels helps determine the effectiveness of the medication. Blood urea nitrogen (BUN) is a test used to assess kidney function and is not specifically related to thyroid function or levothyroxine therapy. Prothrombin time (PT) is a test used to evaluate the clotting ability of the blood and is not directly related to thyroid function or levothyroxine therapy. Arterial blood gases (ABGs) are used to assess oxygen and carbon dioxide levels in the blood and evaluate acid-base balance. ABGs are not specifically related to thyroid function or levothyroxine therapy.