A previously healthy 35-month-old girl was brought to the emergency department with an altered level of consciousness. She had been well until five days prior to presentation, when she developed dysuria, reduced appetite, polyuria, polydipsia, and significant weight loss (from 14 kg to 11 kg). There was no known family history of diabetes mellitus. On admission, her anthropometric measurements were as follows: height 92 cm (25th–50th percentile), weight 11 kg (5th–10th percentile), and BMI-for-age at the 72nd percentile. Her vital signs revealed a temperature of 38°C, heart rate of 160 beats per minute, blood pressure of 95/50 mmHg, and a Glasgow Coma Scale score of 11/15. Physical examination demonstrated delayed capillary refill time (>3 seconds) and weak peripheral pulses, suggestive of poor perfusion.

Capillary blood glucose measurement indicated marked hyperglycemia, prompting confirmatory serum testing. Initial venous blood gas analysis showed: pH 7.26, pCO₂ 32 mmHg, pO₂ 39 mmHg, bicarbonate (HCO₃⁻) 15.8 mmol/L, and base excess −12.6, consistent with metabolic acidosis. A cranial CT scan, performed due to the patient’s decreased level of consciousness, revealed cerebral edema.

Initial management included fluid resuscitation with isotonic saline (10 mL/kg). Subsequent laboratory investigations demonstrated severe hyperglycemia (serum glucose 1124 mg/dL), elevated blood urea nitrogen (71 mg/dL) and creatinine (1.9 mg/dL), hypernatremia (serum sodium 170 mEq/L; corrected sodium 186 mEq/L), and potassium 5.1 mEq/L. The calculated effective serum osmolality was markedly elevated at 402 mOsm/kg. Her urinalysis revealed a specific gravity of 1.010, glucosuria (3+), and trace ketonuria. Repeat venous blood gas analysis following initial fluid resuscitation showed minimal change (pH 7.27, pCO₂ 34.8 mmHg, HCO₃⁻ 15.8 mmol/L).