What test measures average blood sugar levels over a period of 2-3 months?

The test that measures average blood sugar levels over a period of 2-3 months is glycosylated hemoglobin, commonly known as A1c. This test assesses how much glucose has attached to hemoglobin, a protein in red blood cells. Since red blood cells typically have a lifespan of about 120 days, the A1c test reflects the average blood glucose levels for the past two to three months.

This is particularly useful in diagnosing and monitoring diabetes, as it provides a more comprehensive view of glucose control than a single blood sugar measurement. It helps clinicians evaluate the effectiveness of a patient's diabetes management plan over time.

In contrast, the other tests focus on immediate or short-term glucose levels. The fasting blood glucose test measures blood sugar after a period of fasting, while the random blood sugar test checks glucose at any time regardless of meals. The oral glucose tolerance test assesses how well the body processes sugar but is performed over a shorter time frame, not reflecting long-term average levels. These differences highlight why the A1c test is specifically designed for monitoring average blood sugar over the specified months, making it the correct choice.