Understanding Markers of Blood Sugar Control

IS THIS FOR YOU? You’re doing everything right. You’ve decided to finally take control and to pay more attention to your diabetes. You’re checking your blood sugar often at home and at different times of the day. You’re paying close attention to your food choices and being careful on portion sizes. In fact, you’ve been doing so well you can’t wait to see your doctor to prove that your efforts have paid off!

Your glucose levels are way down but, when you do see your doctor, you’re surprised (and a little shocked) to discover that your average control is not as good as you thought it was. Your doctor checked your hemoglobin A1c and is concerned that your average blood sugar may be running too high (or too low). How can that be? Your blood sugars at home have been on target for the last several months. You and your doctor confirm your glucose meter is working properly.

What can be a possible explanation for this? It’s time to learn about some markers of blood sugar control!

HEMOGLOBIN A1C When sugar (glucose) is higher than it should be in blood, it attaches to proteins in the body. This is used as a marker or indicator of blood sugar control.

HERES' HOW IT WORKS : Many different types of cells are found in blood, among them are the red blood cells. They are named “red” blood cells because they contain a protein named hemoglobin [HEE-mo-glo-bin], which gives them the color red. Hemoglobin is the protein responsible for getting oxygen to the body’s tissues.

Because glucose/sugar can easily enter the red blood cells, when blood sugar levels increase, sugar molecules enter the red blood cells and attach to hemoglobin. The higher your blood sugar, the more sugar will enter the red blood cells and will attach to the hemoglobin. Glucose attaches to hemoglobin (also called glycated [gly-kay-ted] hemoglobin).

Measuring A1c allows providers to help patients evaluate their blood sugar levels so that problems related to chronic hyperglycemia [hie-per-gly-SEEM-ee-ah] can be prevented.

Red blood cells live for about 120 days. So, an A1c level reflects the average blood sugar in the last 120 days, but it more closely reflects levels of the last 60 to 90 days.

The A1c value is affected by how long red blood cells have been in the body. Some conditions can result in either a lot of older red blood cells or too many young red blood cells in the body. This can affect the accuracy of the test.

Scenario 1: If red blood cells are old, they’ll be exposed to serum glucose for a longer period of time. This will allow more glucose attachment to hemoglobin, possibly increasing the A1c level. This will make it seem like your average blood sugar level is higher than it really is. It is more likely that you are deficient in iron, folate and/or vitamin B12.

When red blood cells are old and A1c values show blood sugar levels to be higher than reality, insulin regimens can be mistakenly increased. This can cause hypoglycemia. Treatments that are actually working might be readjusted by mistake, and become less effective.

Scenario 2: Other conditions shorten the life span of red blood cells. The body will then produce many young red blood cells, which might lower your A1c level. The A1c level will be low because the red blood cells won’t have been in the body long enough to have glucose attached to them. This will make it seem like your average blood sugar level is lower (better) than it really is. The more common conditions that cause this to happen are hemolytic [heemo-LIT-ic] anemia, sickle cell anemia, and sickle cell trait.

When red blood cells are up and A1c levels are showing that average blood sugar levels are lower than reality, your doctor may wrongly assume that your blood sugar control is great. This could lead to lack of control of your A1c levels, which may cause health problems down the road.

People with chronic kidney disease can have falsely low or falsely high A1c values, making them tough for the doctor to interpret.

A1c is a valuable tool in medical practice and a good indicator of glycemic control that works for most people. However, one should be careful when home blood sugar levels are different from the average glucose value obtained by your doctor measuring A1c.

Other factors that can also affect A1c values are:

  • How A1c is measured, and abnormal hemoglobins.
  • Racial variation: African Americans, Hispanics, and Asians may have naturally higher A1c than whites.
  • Medications. Common ones include:
    1. Erythropoietin [eh-RITH-ro-POY-eh-tin] (this drug causes red blood cells to be created).
    2. Iron, folate, vitamin B12 treatment. Correcting low levels of any of these will make A1c levels change.
    3. The National Glycohemoglobin [gly-ko-HEE-mo-glo-bin] Standardization Program (NGSP) website (www.ngsp.org) contains information about substances that interfere with A1c test results.

If you think your blood sugar is better controlled than what your A1c says, you should discuss this with your doctor. The A1c test may not be the right test for you. By reviewing your medical history, medications, etc., your doctor should be able to determine if it is the right test or not. Luckily, there are other good tests. Some of the more commonly used ones are fructosamine [frook-TOE-sa-meen] and 1,5 AG (Glycomark). No test is perfect, but by talking about your options with your doctor, you should be able to find one that works best for you!

Dr. Lorena Alarcon-Casas Wright is board certified in Internal Medicine and Endocrinology, Diabetes and Metabolism. She is currently a Senior Research Fellow at the University of Washington where she is involved in clinical research, education and patient care. Dr. Wright’s main interests are in the areas of prediabetes, optimal diabetes care and pregnancy complicated by diabetes.