MRCP2-1068

MRCP2-1068

A 15-year-old girl presents to the Emergency department with a four day history of nausea and vomiting. She has a 10 year history of insulin-dependent diabetes mellitus and has had multiple admissions for diabetic ketoacidosis due to poor glycaemic control. On examination, she appears alert and oriented with dry mouth but no loss of skin turgor. Laboratory investigations reveal elevated glucose, ketones, and creatinine, as well as low bicarbonate levels. She is treated with intravenous fluids and insulin, which initially improves her symptoms, but nausea and vomiting resume when fluids are discontinued. Seven days later, her blood biochemistry shows abnormal levels of sodium, potassium, urea, and bicarbonate. What single test would be most useful in determining the cause of these biochemical abnormalities?