A 53 year old woman presents with excessive thirst and increased frequency of urination for 3 months. She sleeps poorly as she has to urinate at least twice each night.

Her medical, surgical and family histories are unremarkable.

A fasting plasma glucose is found to be 80 mg/dL. Her full blood count, renal functions, serum sodium, potassium, chloride and calcium levels, and serum uric acid levels are within normal parameters.