FCA1-0401

FCA1-0401

The Medical Admissions unit receives a 71-year-old woman. She has type 2 diabetes, which she manages with diet, but she has been feeling ill for the past 48 hours. Her pulse rate is 110 beats per minute, her blood pressure is 90/50 mmHg, and she is clinically dehydrated. Her respiratory rate is 20 breaths per minute, and chest auscultation reveals no focal signs. The following are the lab results: Glucose 27.4 mmol/L (3.5-5.5), Ketones 2.5 mmol/L (<0.1), Urinary glucose is zero (dipstick) with ketones. A random blood glucose of 15.3 mmol/L was measured during a visit to the diabetic clinic one month prior to admission, according to her notes, and a urinary dipstick registered a high glucose and ketones++. The discrepancy between plasma and urinary glucose measurements is best explained by which of the following physiological mechanisms?