Question

A 61-year-old woman presents to the clinic for a follow-up visit to review her routine annual laboratory results. She reports feeling generally well, though she mentions a mild, intermittent sense of fatigue over the past few months. She has no significant past medical history and takes no medications. Vital signs include a temperature of 37.0°C (98.6°F), blood pressure of 122/78 mmHg, pulse of 74/min, and respiratory rate of 14/min. Physical examination reveals a well-appearing female with clear lungs, normal heart sounds, and a non-tender abdomen without organomegaly. The laboratory panel from the previous day demonstrates a serum calcium level of 11.3 mg/dL and a normal serum albumin level of 4.1 mg/dL. Her complete blood count and basic metabolic panel are otherwise within normal limits. Which of the following is the most appropriate next step in laboratory evaluation?