Basal Insulin and A1C

In people without diabetes, the pancreas makes small amounts of insulin continuously to cover the body’s constant need for glucose, which is produced by the liver during times of fasting. This is called basal, or background, insulin. If you have diabetes, your pancreas may not make any basal insulin. You have to inject some, or your cells won’t be able to get the glucose out of the bloodstream. They will starve while your blood glucose rises.

But how much basal insulin should you take? How does your doctor know how much you need? As Certified Diabetes Educator (CDE) Gary Scheiner writes, “the level of basal insulin should come as close as possible to matching the liver’s secretion of glucose throughout the day and night.”

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(Note that basal insulin is only for covering the basic glucose produced by the liver. To cover the food you eat, you will need a shorter-acting insulin or some other treatment.)

If you don’t get enough basal insulin, blood glucose will rise, but too much basal insulin can cause hypoglycemia (low blood sugar). Surprisingly, too much basal insulin can also cause higher A1C (a measure of blood glucose levels over the previous 2–3 months). How could this be?

Basal insulin and A1C

Certified Diabetes Educator Joy Pape writes on Diabets Control, “Patient after patient whom I see [with] an elevated A1C often has frequent low glucose levels…. Most think a high A1C means one needs to increase insulin. Not always!

Pape says that continuous glucose monitoring (CGM) often shows that glucose levels go too low, and then rebound to go too high. This rebound is called the Somogyi effect and usually happens at night.

How might you know if a Somogyi rebound is causing higher A1C levels for you? A1C is a combination of two factors: your blood sugar levels after meals (postprandial) and your levels when you haven’t eaten (fasting level). If your postprandial numbers are not too high, but your A1C is, then your fasting level is probably high. This might be due to either not enough basal insulin or too much.

Diabetologist Sandhya Manivannan, MD, warns that many people have undetected low blood sugars at night. “Hypoglycemia…is a hint that someone could be on too much basal insulin.”

Not only are these lows not good for you (and potentially dangerous), but they could cause an artificially low A1C, or a higher one through rebound effects. The only way to know if you’re having these lows and rebounds is with frequent glucose checking in the night, or better yet, with a CGM. Pape says, “Fingersticks are a picture. CGM is the ‘film.’”

It takes work with a doctor or CDE to get basal dose right, and Scheiner say that, until you do, you can’t really get your whole insulin plan fine-tuned. If your A1C does not seem to match with your after-meal numbers, consider asking for CGM monitoring of your basal levels.

Want to learn more about using basal insulin? Read “Getting Down to Basals” and “Tune Into Your Ratio(s).”

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  • RAWLCM

    I was able to get a more consistent glucose level by splitting my basal insulin into equal morning and night doses instead of taking it all at once -under my doctor’s supervision, of course.