What test is commonly used to diagnose diabetes mellitus?

The Hemoglobin A1c test is a common diagnostic tool for diabetes mellitus because it provides an average of blood glucose levels over the past two to three months. This is crucial for identifying individuals with diabetes or those at risk for developing the condition. The test measures the percentage of hemoglobin that is glycated, which occurs when glucose binds to the hemoglobin in red blood cells.

A key reason for the popularity of the A1c test in diabetes diagnosis is that it is not influenced by short-term fluctuations in blood sugar levels that can occur with dietary intake or stress. This makes it a reliable measure to assess long-term glucose control, which is vital in managing diabetes effectively.

Other tests mentioned, such as the complete blood count, blood urea nitrogen, and basic metabolic panel, do not specifically target glucose control or provide the same long-term insight into blood sugar management. Instead, these tests serve different purposes in evaluating a patient's overall health, kidney function, or electrolyte balance, and therefore are not suitable for diagnosing diabetes mellitus directly.