Final answer:
Polydipsia and polyuria with normal blood glucose levels are indicative of diabetes insipidus, not diabetes mellitus, which features high blood sugar levels.
Step-by-step explanation:
Polydipsia (increased thirst) and polyuria (excessive urination) with normal blood glucose levels suggest a condition known as diabetes insipidus, which is distinct from diabetes mellitus. Although diabetes mellitus, whether it's type 1 or type 2, also presents with polyuria and polydipsia, these symptoms are accompanied by high blood glucose levels due to problems with insulin production or cell response to insulin. Diabetes insipidus, however, results from a lack of antidiuretic hormone (ADH) or kidney response to ADH, leading to an inability to concentrate urine, thus the kidneys excrete an abnormally high volume of dilute urine.