A1C Accuracy in Kidney Disease

Why is hemoglobin A1C important?

For people with kidney disease and diabetes, controlling your diabetes is one of the best things that you can do to help prevent further kidney damage, so knowing how well you are controlling your diabetes is very important. The Hemoglobin A1C is a lab test that is frequently used to measure whether or not a person has diabetes or is controlling their diabetes. For people with kidney disease, A1C is not always an accurate measure of how you are managing your diabetes. And to understand why that is, we need to understand what exactly the A1C is measuring a bit better.

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What is hemoglobin A1C?

Hemoglobin A1C, also known as just A1C measures how much glucose is bonded to a protein in your blood called hemoglobin. When we eat, food is broken down into glucose and absorbed into our blood. And while the glucose and hemoglobin are both floating around in your blood, some of that glucose gets attached to the hemoglobin. The more glucose that is attached to the hemoglobin, the higher the A1c will be.

And when I explain hemoglobin A1C to people, I like to use the analogy of one of those cash blowing machines. You know the ones where it’s a big tube of money blowing around and there is a person inside trying to grab as much as they can?

Well, if you have a cash blowing machine that has 1,000 one dollar bills blowing around in it and another machine blowing around only 100 one dollar bills, you’ll probably grab more money if you’re in the machine that has 1,000 bills around, right? The more dollar bills flying around, the easier it is to catch some.

The same principle applies to your hemoglobin A1C. The more glucose in your blood, the easier it is for hemoglobin to grab more glucose. And the more glucose in your blood, the less controlled your diabetes.

Here is a table showing average glucose levels and how they correspond to A1C. The higher the average glucose levels, the higher the A1C.

Now, there is a second component to the A1C, and that is how much time it has to grab glucose. If you think about the money machine example again, let’s say we all decide to go in the machine with 1,000 one dollar bills whirling around. If I gave you a choice between standing in the money machine for two minutes or three minutes, which would you choose? Probably the 3 minutes, right? All things equal, the more time you spend in that machine, the more money you can grab, right?

Same thing with hemoglobin. The more time it spends circulating through your blood, the more glucose it can grab. The average lifespan of hemoglobin in a person without kidney disease is about 3 months, so a normal hemoglobin will have three months to grab glucose.

Why is hemoglobin A1C inaccurate in kidney disease?

There are a few reasons why A1C might not be completely accurate for someone with kidney disease.

  • Hemoglobin spends less time in your blood. The less time that hemoglobin spends in the blood, the less opportunity it has to grab glucose – even if the glucose levels are high! If your average blood glucose level is 183 and the hemoglobin has 3 months to circulate, then your A1C will be roughly 8%. But if your hemoglobin only has 2 months to circulate, then it won’t have as much time to grab glucose, and the hemoglobin A1C will show up lower. The more advanced your kidney disease, the more likely your hemoglobin is spending less time in your blood and the less accurate your A1C will be.
  • Blood transfusions – if you are receiving blood transfusions, then your A1C measurements likely won’t be as accurate. In this case, the new blood being added to your body will have a low A1C, and this will ‘water down’ the hemoglobin A1C of the blood already in your body. This will result in a lower A1C lab result that will not accurately reflect blood sugar control.
  • Erythropoietin stimulating agents – Anemia is a common problem for people with kidney disease, and many people may be put on a medication to stimulate the production of more red blood cells. This has a similar effect as blood transfusions. Your body starts to create lots of new red blood cells that contain fresh hemoglobin that will not have a lot of glucose attached to it. This can ‘water down’ the hemoglobin A1C  and result in a lower A1C lab result that does not accurately reflect blood sugar control.
  • Certain conditions such as inflammation, oxidative stress, and metabolic acidosis can actually cause hemoglobin to grab more glucose. This would theoretically cause the A1C to appear higher than it should be. However, the most common situation in kidney disease is for the A1C to be underestimated, meaning that it is lower than it should be.

Why does inaccurate A1C matter in kidney disease?

For people with kidney disease and diabetes, controlling your diabetes is one of the best things that you can do to help prevent further kidney damage, so knowing how well you are controlling your diabetes is important. If your A1C is inaccurate, it could make you think that your diabetes is better controlled than it really is.

One of the best ways to measure how well your blood sugars are being controlled is to use a Continuous Glucose Monitor. Want to learn more about using a continuous glucose monitor to manage your diabetes and protect your kidneys? Let me know here, and I can send you some more information!

Source: https://pubmed.ncbi.nlm.nih.gov/36272764/

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