HbA1c Test Accuracy

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HbA1c Test Accuracy

If you’ve had diabetes for a while, chances are you’ve become familiar with the HbA1c test — a measure of long-term blood glucose control. Your doctor will most likely order this test at your regular appointments, since it’s considered the most reliable indicator of blood glucose control over the previous 2–3 months. According to current guidelines from the American Diabetes Association, most people should aim for an HbA1c level of 7% or lower — and possibly even lower than that, if your doctor thinks it’s a good idea.

But the HbA1c test isn’t perfect. One potential pitfall of the test is that while it gives a snapshot of average blood glucose levels, it doesn’t account for blood glucose variability. For example, a person with an average blood glucose level of 120 mg/dl could have glucose levels that are close to that level all of the time, or a glucose level of 140 mg/dl for 75% of the time and 60 mg/dl for 25% of the time. Clearly, the first scenario is much better, since it represents a much lower risk of hypoglycemia (low blood glucose). But two people in these different situations would most likely have nearly the same HbA1c level.

Another potential problem with the HbA1c test has come to light only recently. Last month, researchers at Harvard Medical School announced — in a study published in the journal Science Translational Medicine — that based on their findings, the accuracy of the HbA1c test in reflecting average blood glucose levels depends on the age of a person’s red blood cells. The HbA1c test measures the extent to which glucose has become attached to a protein in red blood cells, so if a person has red blood cells that live slightly longer than another person’s, that person will have a higher HbA1c level even if both of them have the same average blood glucose level.

As noted in an article on the study at, the researchers examined the HbA1c test results of 200 participants. After comparing the results to the glucose readings of participants using a continuous glucose monitor, they found that differences in average blood glucose readings of as much as 15 mg/dl could lead to an identical HbA1c reading. These differences were seen in about one third of participants.

The researchers also conducted tests to determine the average age of participants’ red blood cells. The average lifespan of red blood cells is usually about 120 days, but in some people, this period may be slightly longer or shorter — due to factors like nutrition and stress, and certain diseases. Once the researchers took the age of red blood cells into account and adjusted HbA1c results based on this, the number of participants whose blood glucose levels mismatched their HbA1c results by 15 mg/dl or more dropped from about a third to about one in ten.

So according to this study, changing how HbA1c is calculated — by taking a separate measurement of red blood cell age, in addition to the regular test — could improve the accuracy of how closely the test tracks blood glucose levels by as much as 15 mg/dl, or even more in some cases. How do you feel about this idea — do you care how closely your HbA1c level corresponds to your blood glucose levels? Do you think such a potentially small difference would justify making the test more complicated and expensive? Or should any improvement in accuracy be embraced? Leave a comment below!


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