When you talk about your diabetes with your health care team, you’ll often discuss your blood glucose and hemoglobin A1c numbers. What are these tests actually measuring and what do the numbers mean?
Glucose, or sugar, comes from breaking down food into energy for the body. When you eat food, your body turns it into glucose. The glucose travels through your blood. Your body likes to have stable levels of glucose in the blood at all times. Without diabetes, your body is able to adjust the level of glucose in your blood by putting the extra glucose into your cells.
When you have diabetes, this system doesn’t work well. Glucose gets stuck in your blood and it can’t get into your cells. While there are many treatments for diabetes that help you move glucose into your cells, such as nutrition, exercise, medications, and metabolic surgery, none of these cure diabetes. For that reason, we don’t expect that people with diabetes will have the same blood glucose levels as those without diabetes. This is why there are different blood glucose targets for people with and without diabetes.
There are also different blood glucose targets based on whether or not you’ve eaten something recently. A fasting level of blood glucose means you haven’t had anything to eat or drink (besides water) for at least 8 hours. A postprandial level of blood glucose is after you’ve eaten. It’s common to check blood glucose 2 hours after eating for a postprandial level.
Based on all of these factors, here are typical blood glucose targets:
2 Hours after Eating
Person with diabetes
Less than 180 mg/dL
Person without diabetes
Less than 140 mg/dL
You may have individualized blood glucose targets from your diabetes team. When your blood sugar is higher than the target range, this is called hyperglycemia. When you frequently have hyperglycemia, it increases the risk of having complications related to diabetes, such as problems with your heart, eyes, and kidneys.
When your blood sugar is lower than 70 mg/dL, this is called hypoglycemia. You need to treat hypoglycemia right away. Hypoglycemia can lead to death if it is not treated quickly.
Hemoglobin A1C (also called HbA1c, A1C, or glycated hemoglobin)
Hemoglobin is a protein in your red blood cells. Just like glucose, the red blood cells travel through your bloodstream. Some glucose in your bloodstream attaches to the hemoglobin in your red blood cells. When your HbA1c is measured, the test tells you how much glucose is attached to the hemoglobin in your red blood cells. The higher your blood glucose levels, the more glucose you’ll have attached to the hemoglobin, and the higher your HbA1c number will be.
The HbA1c test is technically measuring the percentage of hemoglobin that has glucose attached to it. However, when we’re talking about HbA1c, it’s common to say only the number without the word “percent”. The general goal for people with diabetes is a HbA1c under 7%. You might have an individualized goal from your diabetes team.
Red blood cells live for 2 to 3 months. This means that the HbA1c test gives you an average of your blood glucose levels for the past few months. In other words, the HbA1c test reflects the red blood cells that are living in your body at the time of the test and how much glucose has been attached to them for the past 2 to 3 months. For this reason, it’s common to have your HbA1c tested every 3 months. When you start a new medication or commit to a new nutrition plan, we can’t expect your HbA1c to change drastically in just days or weeks. We have to wait for the current red blood cells to die. The new red blood cells will reflect the changes in your medication or lifestyle.
Why do we measure both blood glucose and HbA1c? The blood glucose test gives us an exact measurement in that moment. It gives us the snapshots of your day to day glucose levels and whether you need support managing any levels that are frequently above or below your targets.
On the other hand, the HbA1c test gives us an average of your blood glucose over the past 2 to 3 months. It gives us the big picture to know whether your treatment plan is helping to consistently keep your blood glucose in its target range.
With a better understanding of these numbers, you might have questions about your blood glucose or HbA1c targets and how to reach them. Be sure to write your questions down so you can discuss them with your diabetes team at your next appointment.