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Every diabetic is admonished to achieve HbA1C levels below 7.0 percent. But what does the glycosylated hemoglobin test really reveal about how well diabetes is managed.

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.

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