MRCP2-4574

A 32-year-old woman comes to the gastroenterology clinic for follow-up. She was diagnosed with coeliac disease 2 years ago and has been experiencing severe fatigue, muscle aches, and weakness in her proximal muscles for the past few months. During the examination, her blood pressure is 112/70 mmHg, and her pulse is regular at 75 beats per minute. Proximal muscle weakness is confirmed.

Lab results show a calcium level of 2.0 mmol/l and an alkaline phosphatase level of 275 IU/l. What is the most useful next investigation?