MRCP2-1159

A 67-year-old man presents to the emergency department with sudden onset epigastric pain that radiates to his back and has been unremitting for the past day. He has also been experiencing headaches, low mood, and nocturia for several months. He appears unwell on examination with dry mucous membranes and tachycardia. Urinalysis shows glucose, protein, and ketones. His blood work reveals elevated glucose, creatinine, and low bicarbonate and albumin levels. Which diagnostic test would be most helpful in determining his diagnosis?