Could Your HbA1c Diabetes Test Be Wrong?

Dr. Sharon Orrange
Dr. Orrange is an Associate Professor of Clinical Medicine in the Division of Geriatric, Hospitalist and General Internal Medicine at the Keck School of Medicine of USC.
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A glycated hemoglobin (HbA1c) is a preferred screening test for diabetes. Done easily with a fingerstick in your physician’s office, it eliminates the need for fasting (not eating) prior to the test. The diagnosis of diabetes is confirmed if two consecutive A1c levels are greater than or equal to 6.5.

What is the HbA1c?

Red blood cells are permeable to glucose (sugar)—so after they enter your circulation, glucose becomes attached to them. The degree to which your red cells become “sugar coated” depends on your blood glucose level. The A1c indicates the average blood sugar level over the lifespan of the red cell—and it lines up with average blood sugar over the previous 2 – 3 months.

Take home message here: your HbA1c will not be affected if you had pizza the night before, unlike a random blood sugar test. But because the A1c is influenced by the total life cycle of your red cells, the levels can be inaccurate in some folks.

Here are some times the HbA1c will not be helpful:

A1c falsely elevated (HIGH)

Your test may tell you that you have diabetes, but you don’t.

A1c falsely decreased (LOWER)

Your test may show that you aren’t diabetic, but you are.

Your A1c will be inaccurate either way (HIGH or LOW)

Well, what can I be tested with if I can’t do HbA1C?

Fructosamine. Diabetes specialists will check blood concentration of a protein called fructosamine to get a longer-term estimate of your glycemic/sugar control. This gives them a better idea of your sugar levels, over random or fasting blood glucose.

Dr O.

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