An 18-year-old female was taken to the emergency room in coma. Her parents noticed that she had polydipsia, polyuria, and rapid weight loss which started approximately 1 month ago and had worsened in the last week. She had not been taking any medications and the clinical history was otherwise unremarkable. On examination, breathing was deep and rapid (Kussmaul respiration), pulse rate was 100 beats per minute, and blood pressure 110/70 mmHg; she also had signs of dehydration. She was drowsy and confused. Rapid hematology and biochemical tests showed hematocrit 44%, hemoglobin 13 g/dl (140 g/L), white blood cell count 12,000/ μl, glucose 520 mg/dl (28.9 mmol/L), urea 50 mg/dl (8.5 mmol/L), creatinine 0.8 mg/dl (70.7 μmol/L), Na+ 148 mEq/L, K+ 4.6 mEq/L, PO4 3-2.0 mEq/L (0.64 mmol/L), and Cl− 112 mmol/L. Arterial pH was 7.0, PO 2 98 mmHg, PCO 2 25 mmHg, HCO 3−12 mEq/L, and O 2 sat 98%. What is your diagnosis? Which additional biochemical tests are required to confirm the diagnosis? How will you manage this patient?