New official guidelines for diabetes screening and diagnosis includes a blood test, which gives a person's average blood glucose level over the previous 2-3 months.
Called the A1C test, it has been in use since the late 1970s as a way to get a snapshot of how well glucose control is going in people with diabetes.
But only in the last 15 years has its use and scoring became more standardized and reproducible from place to place and time to time than other diabetes blood glucose tests.
Now, the A1C test is given a prominent role in the 2010 guidelines for diabetes screening, diagnosis and prevention.
Researchers have recommended that the A1C be used to identify people with "pre-diabetes," those at increased risk for developing the type 2 form of disease.
Unlike type 1 diabetes with its sudden onset, type 2 develops gradually and without symptoms. But its damage to health and longevity can be equally severe.
Dr. John Buse, professor of medicine and endocrinology chief at the University of North Carolina at Chapel Hill has strongly recommended the A1C assay for diabetes diagnosis and for identifying people at high risk for diabetes.
"One big advantage of the A1C test is that it doesn't require fasting. The patient can come in any day, at any time. It's also not as skittish as the older blood sugar test which can be increased by the kind of complaints that often bring people to the doctor like pain or infection. The A1C won't be interfered with that way because it looks at your average blood sugar over 2-3 months," he said.
The test measures the percentage of glycated hemoglobin, or A1C, in the blood. Hemoglobin, a protein found in red blood cells, carries oxygen from the lungs to all the cells of the body.
In diabetes, excess glucose in the bloodstream enters red blood cells and links up (glycates) with molecules of hemoglobin. The more excess glucose in your blood, the more hemoglobin gets glycated.
By measuring the percentage of A1C in the blood, you get an overview of your average blood glucose level for the past few months.
This record changes as old red blood cells in your body die and new red blood cells (with fresh hemoglobin) replace them.
The amount of A1C in your blood reflects blood sugar control for the past 120 days, or the lifespan of a red blood cell.
In a person who does not have diabetes, about 5 percent of all haemoglobin is glycated.
For someone with diabetes and high blood glucose levels, the A1C level is higher than normal.
How high the A1C level rises depends on what the average blood glucose level was during the past weeks and months.
Levels can range from normal to as high as 25 percent if diabetes is horribly out of control for a long time.
The findings have been detailed in the annual supplement to the journal Diabetes Care.