Final answer:
Based on Susan's symptoms of excess thirst, glycosuria, and decreased urine pH, she most likely has diabetes mellitus, a condition characterized by high blood glucose levels and the body's inability to properly utilize glucose.
Step-by-step explanation:
The symptoms presented by Susan, such as excess thirst, glycosuria (presence of glucose in her urine), and decreased urine pH, point towards a condition affecting her blood sugar regulation. Collectively, the symptoms of excess urination (polyuria), excessive thirst (polydipsia), and the presence of glucose in the urine suggest a strong likelihood of diabetes mellitus. In this condition, the body's cells are unable to efficiently utilize glucose due to inadequate insulin or insulin action, leading to elevated blood glucose levels (hyperglycemia) and subsequent excretion of glucose in the urine. On the other hand, diabetes insipidus is characterized by chronic underproduction of antidiuretic hormone (ADH) or a mutation in the ADH receptor, which leads to a loss of water through urine and consequent increased thirst, without the presence of glucose in the urine.
Given Susan's specific manifestation of glycosuria, the final diagnosis would likely be diabetes mellitus rather than diabetes insipidus. This is further supported by the abnormal urine pH, which is often affected by the presence of acidic substances like ketone bodies, which can be produced in higher amounts in individuals with uncontrolled diabetes mellitus.