What is determined by the HbA1c test?

The HbA1c test measures the average blood sugar levels over the past three months, which reflects the long-term control of blood glucose in individuals with diabetes. This test works by assessing the percentage of glycated hemoglobin in the blood, which occurs when glucose binds to hemoglobin in red blood cells. Since red blood cells have a lifespan of about three months, HbA1c provides a reliable indication of blood sugar levels over that period.

It is important to understand that the other choices either refer to shorter time frames or different aspects of diabetes management. For instance, while serum glucose levels can fluctuate daily or even hourly, they don’t represent the longer-term management that HbA1c assesses. Furthermore, the current blood sugar level is a snapshot, typically measured through fingerstick tests, rather than a comprehensive view over weeks or months. Lastly, the effectiveness of insulin injections would involve monitoring various factors, including but not limited to blood sugar readings and HbA1c levels, rather than being exclusively determined by the HbA1c test alone. Thus, the choice stating the average blood sugar level over the past three months accurately captures the primary purpose of the HbA1c test.