Which of the following tests would most likely be used to detect diabetes mellitus?

The detection of diabetes mellitus commonly involves testing for the presence of glucose in the urine, making urinalysis for glucose the most relevant test in this context. In individuals with diabetes, especially when blood glucose levels exceed the renal threshold for glucose reabsorption, glucose spills over into the urine. Therefore, a urinalysis revealing elevated glucose levels can be a strong indicator of diabetes mellitus.

While testing for ketones can provide additional information about metabolic processes in diabetic individuals, particularly in the context of diabetic ketoacidosis, it is not primarily used for the initial diagnosis of diabetes. Other tests listed, such as a pregnancy test and a blood urea nitrogen test, do not directly correlate with diagnosing diabetes mellitus. The focus of using urinalysis for glucose is pivotal in early diagnosis, monitoring, and assessing the effectiveness of treatment for diabetes.