Review Question - QID 214817

A 6-year-old girl is brought to the pediatrician by her father for lethargy and polyuria. He states that over the past few months, she has been taking multiple naps throughout the day. She was previously toilet trained but has recently begun urinating in the bed again. The father also reports that the patient complains she is thirsty all of the time. The patient denies fever, chills, constipation, or diarrhea. Her father says she seems to eat a lot as well, but her BMI is 18.5 kg/m^2. She has no past medical history and takes no medications. Her temperature is 98.6°F (37.0°C), blood pressure is 90/50 mmHg, pulse is 105/min, and respirations are 25/min. A urinalysis is obtained, which reveals glucose and ketones. In addition to testing a fasting blood glucose level, which of the following is the most appropriate antibody to test for in this patient?