How Often to Check A1C

by David Mendosa Patient Advocate

All of us who have diabetes regularly get our A1C checked. Few of us check it often enough.

The A1C is the best way we have to show how well we are managing our disease. It's a simple test that we can perform at home or at a doctor's office or lab.

Just like the fingerstick tests that we use for spot checking our blood sugar levels before or after meals, the A1C test uses a small drop of blood. But the A1C measures our sugar level over a lot longer time.

How much longer is the question. The answer to that question can tell us how often that we need to check our A1C level.

The A1C test measures the percentage of glycated hemoglobin, also known as HbA1C, in our blood. We need to check our A1C level "twice a year at a minimum or more frequently when necessary," is the advice that the American Diabetes Association offers in its "A1C" article. That's because "the A1C test measures your average blood glucose control for the past 2 or 3 months."

For a long time I've wondered why the ADA isn't more specific about the time period that the A1C test measures. When I started using the A1CNow SelfCheck that finally became available three years ago so we can now check our A1C at home, I started to research this question. The patient insert that comes with it led me to a big book generally considered to be the definitive reference for clinical chemistry, which explains what's going on with the A1C.

The book is Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 5th edition, 2011, edited by Carl A. Burtis et al. This massive volume has 2,238 pages and weighs 10 pounds. I could have bought it for about $250, but instead I borrowed it from my local library on interlibrary loan. In seven of those pages, 1141-1147, the book explains the A1C.

How much glycated hemoglobin we have in our blood depends first on the lifespan of our red blood cells. The "average lifespan is 120 days," the book says, which is of course four months.

But the glycated hemoglobin in our blood is also "directly proportional to the concentration of glucose in our blood" and "represents integrated values for glucose over the preceding 8 to 12 weeks." Most people seem to think that our levels at any time during this two to three month period are equal. But they aren't.

"More recent values," the book continues, "provid[e] a larger contribution than earlier values." How much more?

"The plasma glucose in the preceding 1 month determines 50% of the HbA1C, whereas days 60 to 120 determine only 25%," it says on page 1,442. This is the key statement and the one that prompted me to change my testing strategy.

Since half of the A1C level comes during the previous month, it makes sense to check our A1C much more often than the ADA's recommendation. In fact, I now check my level every month.

Even though I keep my level in tight control, I have been surprised to see how much if varies. A couple of months ago my level was 5.1, but last month it had shot up to 5.5. This month it's back down to 5.1.

I use the A1CNow device to check at home. As a result I don't need to go to the trouble and expense of going to a doctor's office or a lab for testing. I get 10 tests for $129 from That's less than $13 per test.

Since I test my A1C often and regularly, I appreciate that measuring my level actually changes what I do. The "Observer Effect" show that when we watch something, we will also change something about it. By watching my A1C level more closely, I have therefore changed my health for the better.

David Mendosa
Meet Our Writer
David Mendosa

David Mendosa was a journalist who learned in 1994 that he had type 2 diabetes, which he wrote about exclusively. He died in May 2017 after a short illness unrelated to diabetes. He wrote thousands of diabetes articles, two books about it, created one of the first diabetes websites, and published a monthly newsletter, “Diabetes Update.” His very low-carbohydrate diet, A1C level of 5.3, and BMI of 19.8 kept his diabetes in remission without any drugs until his death.