The A1C test is our best scorecard to show how well we are controlling our diabetes. It measures how much glucose has been sticking to our red blood cells for the previous two or three months. Since our bodies replace each red blood cell with a new one every four months, this test tells us the average of how high our glucose levels have been during the life of the cells.

The experts recommend that we should get our A1C level tested at least twice a year. People who take insulin need to get it...