A 26-year-old female with type 1 diabetes mellitus (T1DM) discontinued insulin therapy for 3 days due to reduced appetite from a cold. She suddenly developed coma, Kussmaul breathing, poor skin turgor, thready rapid pulse, decreased blood pressure (BP), reduced urine output, blood glucose 33.3 mmol/L, elevated blood urea nitrogen (BUN) and creatinine (Cr), white blood cell (WBC) count 15×10<sup>9</sup>/L, neutrophils 86%, strongly positive urine glucose and ketones. The most likely diagnosis is: