Review Question - QID 213826

A 27-year-old man with a past medical history of schizophrenia and bipolar disorder, well controlled on risperidone and lithium, presents to his primary care physician for a wellness appointment. He states he feels well and has no complaints at the moment other than a mild cough and runny nose. The patient was seen 2 days ago for increased urinary frequency but otherwise has nothing new to report. His past medical history is also notable for type I diabetes, anxiety, and substance abuse. His temperature is 98.4°F (36.9°C), blood pressure is 135/84 mmHg, pulse is 90/min, respirations are 21/min, and oxygen saturation is 94% on room air. Laboratory studies are ordered as seen below.

Hemoglobin: 13 g/dL
Hematocrit: 39%
Leukocyte count: 9,500/mm^3 with normal differential
Platelet count: 196,000/mm^3

Serum:
Na+: 119 mEq/L
Cl-: 101 mEq/L
K+: 4.4 mEq/L
HCO3-: 22 mEq/L
BUN: 14 mg/dL
Glucose: 154 mg/dL
Creatinine: 1.5 mg/dL
Ca2+: 10.0 mg/dL

Urine:
Color: Clear
Glucose: Trace
Ketones: Negative
Blood: Negative
Protein: 1+
Specific gravity: 1.000

Which of the following is the most likely diagnosis?