How Reliable Is A1c Test for Diabetes Screening?

Diabetes and Pitfalls of A1c Test

Majid Ali, M.D.

The A1c test a useful blood test that indicates the average of blood glucose levels during the preceding 80 to 100 days. It measures the percentage of a blood protein that becomes “sticky” due to sugar attached to it. The test value rises with the rising levels of blood sugar (glucose).

In healthy people, 5 to 5.5 percent of hemoglobin is sticky with sugar (glycated hemoglobin is the scientific term for it). A value of 6.5* or higher on more than two occasions is accepted as a valid criterion for diabetic diagnosis. The red blood cells have a life span of about 120 days and that explains the value of the A1c test in assessing blood glucose levsls over a period of 80-100 days.

The Value and Pitfalls of A1c Test

In general, the A1c test is useful for monitoring the success of diabetes treatment A value of 5.6% or less is considered optimal. The American Diabetes Association (ADA) recommends that every diabetic should have an A1C test done a minimum of twice a year, with more frequent testing for those with poor control or changes in treatment. I use this test more often.

It is a mistake to rely on the A1c test to exclude the diagnosis of diabetes in the initial screening. There are simply far too many errors made in such testing. I illustrate my point with a case study.

A Case Study

Just yesterday, I saw well-informed man in his late sixties. His fasting blood sugar was in the normal lab range and A1 test was 5.1%. Based on these values, none of his ologists had any reason to suspect diabetes. In my view, fasting blood sugar should be banned for screening for diabetes. The real test is insulin. His thee-hour insulin profile revealed insulin toxicity (with peak value almost seven times as high as the optimal value of 25 units).His blood sugar values were above 200 in two of the four blood samples and established the diagnosis of diabetes using the criteria of the American Diabetes Association. He was startled when I told him he had diabetes.

“But I have been seeing my doctors regularly for years and my A1c and fasting blood sugar tests have been perfect. How can I be suddenly diabetic?” he asked.

“No, you didn’t suddenly become diabetic,” I replied.

“No?” he frowned.

“No. If some had done a three-hour insulin test for you three years ago, almost certainly they would have diagnosed pre-diabetes.”

“Then why didn’t they do the test?”

“Doctors rarely do an insulin test.”


“Because that is not the prevailing standard.”

“Why isn’t it so?”

“Because the American Diabetes Association does not say it should be.”

“Why is that so?”

“Can you guess?” I asked.

“Could it be that there is no money in it? The Diabetic Association gets its money from companies that sell diabetes drugs?”

“Your guess is as good as mine,” I replied.

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