What test should be performed for a patient presenting with polydipsia, polyuria, and polyphagia?

The HbA1c test is specifically used to assess average blood glucose levels over the past two to three months. In the context of a patient showing symptoms such as polydipsia (excessive thirst), polyuria (excessive urination), and polyphagia (excessive hunger), these symptoms are indicative of diabetes or a condition associated with high blood sugar levels. The HbA1c test is a critical tool for diagnosing diabetes and monitoring long-term glucose control, making it directly relevant to the symptoms presented by the patient.

In comparison, while the glucose tolerance test is also relevant for assessing how the body processes glucose, it is typically used in specific scenarios, such as during pregnancy or for diagnosing gestational diabetes. The blood urea nitrogen test is more focused on assessing kidney function, and the thyroid function test evaluates thyroid health and would not directly assess glucose metabolism or diabetes. Thus, the utilization of the HbA1c test in this case aligns perfectly with the need to evaluate the patient's glycemic control and confirm or rule out a diagnosis of diabetes.