Hemoglobin A1C: What It Reveals About Diabetes Control, and What It Doesn't

Thousands of endocrinologists tell their diabetic patients that HbA1C measurement is a kind of diabetic truth detector. Even if they get good blood sugar numbers when they are fasting, glycosylated hemoglobin A1C levels will reveal if their blood sugar levels are soaring after meals and only slowly falling back to more nearly normal levels during sleep. But does HbA1C really reveal the truth about how well a diabetic is sticking to plan?

What Is HbA1C?

HbA1C is an acronym for "hemoglobin A1C." Hemoglobin is the iron-rich molecule that red blood cells use to transport oxygen in the bloodstream. Hemoglobin A is "adult" hemoglobin, so designated to distinguish it from a slightly different kind of hemoglobin, hemoglobin F, which transports oxygen in the fetal bloodstream before birth. "Adult" hemoglobin appears in infants, children, and adults. A1C is adult hemoglobin that has been modified by attaching itself to a sugar. When blood glucose levels are high, glucose molecules "hitch a ride" by forming a complex with the amino acid valine at the end of the hemoglobin molecule. Once this bond is formed, the sugar remains attached to HbA1C for the life of the red blood cell that carries it. The higher the levels of sugar in the bloodstream go, the higher the percentage of hemoglobin that is attached to a sugar, so HbA1C  numbers can be used to estimate an average blood glucose level over a period of about 90 days, the average life of a red blood cell.

Is HbA1C The Same Thing As Glycosylated Hemoglobin?

In everyday usage, HbA1C is said to be "glycosylated" hemoglobin, hemoglobin that is attached to a glucose group. Strictly speaking, the process of binding glucose to hemoglobin occurs without the help of an enzyme, so a more technically correct but less frequently used term for HbA1C is "glycated" hemoglobin.

What Does a HbA1C Test Reveal?

There's nothing that a HbA1C test uncovers that isn't better described by taking blood sugar levels several times a day. HbA1C only reveals an "average" blood sugar levels. It doesn't uncover unusual highs and lows during the day.

For instance, some diabetics (usually type 2 diabetics who have only recently developed the disease) still have the ability to release enough insulin overnight to bring blood sugar levels down to normal, but don't still have the ability to release enough insulin quickly to normalize postprandial (after-meal) blood glucose. If the only time they take their blood sugar levels is first thing in the morning, they only see their numbers at their best. An HbA1C test would point out the need for changes in diet or medication to keep sugars down during the rest of the day. They may need more medication and to eat less carbohydrate.

Other type 2 diabetics experience something called the dawn phenomenon. About two hours before sunrise, their bodies begin to "rev up" to get ready for wakefulness. Their adrenal glands release cortisol, which stimulates the liver to release glucose from the stored fuel glycogen. They are ready to swing into action as soon as they wake up. The dawn phenomenon may occur as early as 2 am or as late as 8 am, depending on the time of sunrise.

These diabetics may be doing better with their program than just their fasting blood sugar levels show. They may reduce their risk of hypoglycemia by taking less medication and eating more carbohydrate.

What Truths About Diabetes Does HbA1C Reveal?

Referring to HbA1C as a "lie detector" suggests that diabetics aren't facing the truth about their disease. Often they are. They just aren't taking their blood sugar levels often enough or at the right time of day. Ideally, every diabetic would test before breakfast, about two hours after each meal, and before going to bed, plus before and after exercise. Doing this much diabetic testing reveals information an HbA1C test never can. But since most diabetics don't test that much (in part because glucose test strips are expensive), HbA1C can point the way to helpful changes.

However, HbA1C testing isn't perfect. Here are some considerations that your nurse practitioner or old-school doctor may overlook:

• The HbA1C levels chart uses a mathematical formula for converting HbA1C levels to average glucose levels.(The formula used in the USA has an additional step that converts mmol/L to mg/dl.) It assumes that red blood cells live for 100 days. However, there is a range of lifespans for red blood cells of about 85 to 115 days. If your red blood cells turn over more quickly than expected (which doesn't necessarily mean there is anything wrong with your blood), your HbA1C will be lower than your true average blood sugar levels would predict. If your red blood cells turn over more slowly than expected (which also doesn't necessarily mean there is anything wrong with your blood), your HbA1C levels will be higher than your true average blood sugar levels would predict. If you have fast turnover, your doctor may give you less medicine than you really need. If you have slow turnover, your doctor may give you more medicine than you really need. To get the right amount of medication, you and your doctor need to know your highs and your lows, not just your average level.
• Sickle cell disease may require different methods to monitor long-term blood sugar control. Infants and people who have persistence of fetal hemoglobin may not have the kind of hemoglobin that glycates with blood glucose and get false negative results, appearing to have good blood sugar control when they do not. (All of these conditions are relatively rare, and you would likely know if you have them.)

What can you expect if your HbA1C levels are high? In the United States, there are some new recommendations for diabetics with high blood sugar levels that you would not have heard in the past. Below we are listed a few healthy choices that lower HbA1c: 

• If your HbA1C is over 7.0 percent and your BMI is over 40 (that is, you are "morbidly obese"), your doctor will recommend bariatric surgery, such as Roux-en-Y gastric bypass, gastric resectioning, or a lap band. These procedures often result in nearly immediate remission from diabetes. It is less expensive for your insurance company to pay for your weight reduction surgery than it is to pay for diabetes care. However, if your body does not produce insulin, you will still have diabetes even after the surgery. Many doctors fail to consider that type 2 diabetics can become insulin-dependent over time.
• If your HbA1C is over 7.0 percent, your doctor may refer you to an endocrinologist to get an insulin pump. The newer models have continuous glucose monitoring that allows you to correct blood sugar problems as soon as they occur. Insulin pumps are now recommended for both type 1 and type 2 diabetics.