Problem: A 32-year-old man who has been taking olanzapine for bipolar affective disorder presents to the clinic with concerns about weight gain. He requests to transition treatment to a different medication. After discussing the risks and benefits of multiple medication options, he is started on valproate. Which of the following must be monitored in this patient following the medication change? A. Platelet count B. Serum potassium C. Serum creatinine D. Thyroid-stimulating hormone