PRESENTATION

L.C., a 25-year-old white woman, presented to the Emergency Department reporting that she was in good health until ~ 3 weeks ago, when she began experiencing polyuria and polydipsia. She had had an unintentional weight loss of ~ 10 lb in the past 2 months.

She denied visual disturbances, nausea, vomiting, abdominal pain, dysuria, history of the same symptoms, and recent illness. She also denied alcohol, tobacco, and illicit drug use. Her medications included only oral birth control pills, and she was a competitive volleyball player. Family history was negative for diabetes, hypertension, coronary artery disease, and autoimmune diseases.

Physical exam revealed a blood pressure of 129/82 mmHg, pulse of 88 bpm, and respiration rate of 20 breaths per minute. L.C.'s weight was 62 kg, and her BMI was 21 kg/m². She seemed healthy and aware. Her eyes, throat, and thyroid were normal, and her neck was negative for lymphadenopathy. She had a regular heart rate and rhythm, negative for murmurs, rubs, or gallops, with normal first and second heart sounds. Lungs were clear with normal respirations. Abdominal exam revealed normal breath sounds and no tenderness, guarding, or rebound. Extremities were normal, and neurological motor and sensory functioning was intact.

Her fingerstick glucose on admission was 571 mg/dl, and subsequently measured serum glucose was 617 mg/dl. Testing revealed a sodium level of 133 mEq/l (normal 135–145), potassium of 4.0 mEq/l (normal 3.5–5.0), chloride of 99 mEq/l (normal 96–108), carbon dioxide of 25 mEq/l (normal 21–30), blood urea nitrogen …