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2 How to interpret an A1C score

THE FACTS ARE IN

Since 1987, research has proven that blood glucose numbers are directly related to future diabetes complications. The landmark Diabetes Control and Complications Trial (DCCT) provided clear evidence that poor glucose control increases the risk of certain types of diabetes complications, including eye, kidney, and nerve damage in those with type 1 diabetes. Other studies followed individuals with type 2 diabetes and demonstrated that lowering average blood glucose could reduce similar complications. For both forms of diabetes, better blood glucose control over time means less chance of complications.

Blood glucose numbers change minute by minute. There are 1440 minutes in a day, so if you want a continuous snapshot of your blood glucose, you’re in for a lot of finger pricks (or a continuous glucose monitor, which we’ll discuss later). Fortunately, there is a test that will show you what your average blood glucose levels have been over a 3-month period of time. The Hemoglobin A1_C (A1C) test is a blood test that measures what your average blood glucose has been for the last 90–120 days. Some other names you may hear or see for this type of test are “glycohe-moglobin,” “HbA1c,” or simply “your percentage.” The preferred reference is “A1C.” This number is an important figure in your diabetes control game plan. Single glucose checks are important, but they can sometimes be misleading. Nothing gives you a better understanding of your overall diabetes control than your A1C.

WHAT IS AN A1C TEST?

A1C is short for a type of hemoglobin, which is a protein found inside your red blood cells. Hemoglobin performs several essential functions, such as carrying oxygen to the cells in your body. It also carries glucose. An A1C check looks at the amount of this glucose to determine your average blood glucose.

To understand how this test works, imagine your arteries and veins as structures forming highways though which liquids and solids can travel. Now imagine that your blood is the traffic on these highways. Blood isn’t just a uniform liquid—it contains a variety of types of cells within its liquid mass, and red blood cells are one of the cell types present. As blood moves throughout your body, the glucose that is also present in the liquid highway will stick to the red blood cell. In other words, it binds, or “glyco-sylates” with the blood cell’s hemoglobin. The more glucose that is in the blood, the more glucose will be found sticking to the hemoglobin. Since the red blood cell lives about 90 days, an A1C test involves looking at mature red blood cells and seeing how much glucose is found sticking to them. The amount is measured in terms of a percentage. For example, an A1C result of 6% means that 6% of the hemoglobin tested has glucose stuck to it.

Keep in mind that there are some circumstances that can affect the accuracy of an A1C result. If you have recently had a blood transfusion, suffered significant blood loss, or you suffer from some forms of anemia you should discuss your condition with your health care provider.

WHAT IS NORMAL?

Depending on the laboratory your physician uses, the normal range of an A1C level is about 4–6%. Check with your physician about what reference range is used, as it is normal to see some variation between laboratory reports, depending on how the analysis is performed. A 4–6% A1C level compares to an average blood glucose level of approximately 70–120 mg/dl, which is considered to be “normal.”

The American Diabetes Association recommends people with diabetes keep their A1C levels below 7% (lower for some), which is a glucose reading of approximately 150 mg/dl on average over a 2–3 month period. (The American Association of Clinical Endocri-nologists supports a slightly lower goal of less than 6.5%, equal to about 140 mg/dl over the same period of time.) Discuss your own target with your health care team. There may be times when your target might need to change (during pregnancy, when treated for other health problems, etc.).

THE WORD “AVERAGE” IS KEY

While an A1C check provides great information, it is not a replacement for daily blood glucose testing. Your daily tests should be reviewed alongside an A1C test to help you understand your daily and overall control. Because A1C is an average, it will not show if you are having problems with hypoglycemia or experiencing unstable readings. It is an important test, but trends in your daily blood glucose cannot be identifed by A1C results alone.

WHERE DO YOU HAVE AN A1C CHECK DONE?

A1C checks are usually done at your doctor’s office, either with equipment on the premises or through a blood sample that is drawn and sent to a laboratory. The result will be sent to the office in a few days to a week. Make sure you get the result and discuss it with your health care providers.

HOW OFTEN SHOULD AN A1C CHECK BE DONE?

The American Diabetes Association currently recommends you have an A1C done twice a year if you are meeting treatment goals and quarterly (every 3 months) if your therapy has changed, or you’re not meeting treatment goals. An A1C will not generally be repeated any sooner than 2 months from the last check unless special circumstances warrant it.

ESTIMATED AVERAGE GLUCOSE

The term estimated average glucose, or eAG for short, is a new way of showing average blood glucose information in the same units (mg/dl) that people are used to seeing on their meters and glucose lab reports, rather than using a percentage like A1C. A1C percentage is sometimes confusing to people, so having your results in terms of a meter value may make the information more realistic and intriguing. Still, it’s simply a different way of showing the same thing—your average glucose over a period of months.

IS YOUR A1C THE SAME AS YOUR eAG?

Not exactly, but it is another way to interpret your control. The eAG will soon be the standard reporting value for health care providers and patients, so you should know how the two values relate to one another. The following is a chart that shows how the two results compare:

IS THE “AVERAGE” REPORTED ON YOUR BLOOD GLUCOSE METER THE SAME AS eAG?

No. The “average” on your meter only reflects the average from the readings you performed. If you only check a few times a day like most people, you only have a few points of data, and not the constant data that’s represented by an eAG or A1C check. The eAG reflects what your blood glucose readings were 24/7 for 3 months.

ONCE YOU HAVE YOUR RESULT

YOUR A1C IS HIGHER THAN 7%. WHAT NOW?

If your test result is higher than your target, immediately discuss with your health care providers what you can do to improve your results in the future. Don’t wait until the next visit! Consider your management plan and ask yourself:

HOW DO YOU CALCULATE YOUR eAG?

You can calculate your eAG using your current A1C result. The formula is as follows:

(28.7 x A1C) — 46.7 = eAG

It’s probably been a while since math class, so an example to illustrate may make it more clear. Let’s say your A1C is 8.2%. For the formula, you treat your A1C result simply as a number and not a percentage. So to calculate your eAG, you would first multiply 28.7 by 8.2 (your A1C):

28.7 x 8.2 = 235.34

Now, you would take this number, 235.34, and subtract 46.7:

235.34–46.7 = 188.64

Then just round up to the nearest whole number, 189, and you have your eAG. In this case, that would be an average blood glucose of 189 mg/dl over a 3-month period. Seeing this should illustrate how eAG is useful. If your doctor says you have an A1C of 8.2%, you probably realize that is high, but it can also be just another number. However, if your doctor says your blood glucose level averages 189 mg/dl, you have a much more concrete idea of what that means. Mostly, it means you’ve got some work to do!

Is your nutrition plan working out?

Are you consistent with your activity plan?

Are you following prescribed medication schedules?

Are there other factors contributing to your control (for example, stress, other health problems, other medications, chronic pain)?

Learn what options your health care providers have to suggest. A high A1C is not simply your fault; it is a problem to be dealt with by you and your health care team.

WHAT IF YOUR SELF GLUCOSE CHECKS DON’T MATCH YOUR A1C?

It is possible your blood glucose meter may need to be replaced, or you’re not following the manufacturer’s guidelines. However, it’s more likely that the variation comes from the different nature of each test. An A1C only reports an average—it cannot show daily fluctuations. Conversely, you may need to do your self glucose checks at different times of the day. Always checking at the same times of day will limit your ability to fully understand your glucose levels over a 24-hour period.

Remember, an A1C result of 7% compares to a blood glucose average of about 150 mg/dl. Think of how many different ways you can mathematically achieve this average, even with just two blood glucose numbers obtained each day during a month. Consider the individuals below:

All four of these individuals have the same A1C, yet their control is obviously not the same. Jill and Jane are experiencing big, out-of-control swings, and Joe and John are not consistently in the 70–140 mg/dl range. Having this type of information can put your A1C results into perspective.

WILL CONTINUOUS GLUCOSE MONITORING REPLACE A1C?

Continuous glucose monitoring (CGM) appears to be the future of self blood glucose testing. By using a device that continually checks blood glucose levels, these systems provide a complete view of levels throughout the day, improving glucose management and overall self-care. However, CGM devices aren’t perfect yet and many are expensive or hard to get; more work certainly needs to be done. Whether they will replace A1C tests remains to be seen, but it’s hard to imagine that an overall glucose snapshot of a 2–3 month period won’t be useful in the future. Likely, CGM will be an excellent tool to use alongside an A1C check. For now, all individuals with diabetes, whether they use a meter, or CGM devices, should have an A1C check to be evaluated alongside daily readings, whether from a meter or a properly calibrated CGM device.

DO YOU STILL NEED TO KEEP A BLOOD GLUCOSE LOG BOOK?

There’s no replacement for a well-kept glucose log book. Always take your logbook (or a meter with a memory function) to appointments. Ask every member of your health care team to review the information, including your educator, nurse, pharmacist, or dietitian. Compare your logbook results with the A1C results on a daily, weekly, or monthly basis and not just every 2–3 months.

MORE RESOURCES TO EXPLORE

BOOKS

Diabetes A to Z: What You Need to Know About Diabetes—Simply Put, 5th edition. American Diabetes Association; Alexandria, VA, 2003.

WEBSITES

American Diabetes Association Website ……. WWW.DIABETES.ORG