Diabetes Forecast

Can Meds Distort My A1C?

My blood glucose levels are in the range of 160 to 190 mg/dl, but my A1C is 5.3 percent, which seems too low. Could my HIV medications be affecting the A1C results? Name Withheld

Craig Williams, PharmD, responds:

Very few things can interfere with the A1C test to give a falsely high or low value. Fortunately, no commonly used medication, including those for HIV, is known to throw off A1C results.

A1C inaccuracies are rare and usually stem from abnormalities in hemoglobin, the part of a red blood cell that gets "glycated" with glucose to form the A1C in the bloodstream. In certain types of anemia, the interaction between hemoglobin and blood glucose is not normal. The laboratory doing the A1C test can often work out these interferences, however, and so the risk of an inaccurate A1C result being reported to a patient or doctor is very, very low.

There are other, practical reasons why an A1C and average glucose readings may not match up, though. Probably the most common is that a person may test blood glucose at just one time of the day and not get a good picture of his or her 24-hour control. For example, if your blood glucose runs high in the morning, and that is always when you check, then your A1C may seem to be falsely low.

In your case, an A1C of 5.3 does seem falsely low for average blood glucose in the 160-to-190 range. A good way to compare an estimated average glucose (eAG) with an A1C is to plug the measured A1C value into the estimated average glucose calculator at professional.diabetes.org/glucosecalculator.aspx. The eAG for an A1C of 5.3 percent is 105 mg/dl. (A way to do the conversion yourself is to subtract 2 from the A1C value, then multiply by 30. In this case, 5.3 minus 2 is 3.3. Multiply 3.3 by 30, and the result is 99 mg/dl, roughly the same.) So, the A1C of 5.3 does seem too low for blood sugars of 160 to 190 mg/dl. It's also possible that your blood glucose meter is inaccurate or that the A1C might be off if it was performed with a "point of care" machine, which uses blood from a finger prick instead of a regular blood draw that is sent to a lab. These machines can provide accurate results but are prone to operator error and don't spot hemoglobin abnormalities as lab tests do.

The first step for anyone whose A1C and blood glucose tests don't match is to check the meter's accuracy. Do this by testing with another meter at the same time (preferably one in your doctor's office) and comparing the results. If the meter isn't at fault, make sure to test your blood glucose at different times of day. If that doesn't explain the mismatch, then the A1C test should be repeated in several weeks. If the inconsistency persists, ask your doctor's office or laboratory to check for possible problems in the A1C test.



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