A1C Test for Diabetes

What is a hemoglobin A1c?

A1c defined
Red blood cells that circulate in the body live for about three months before they die. Sugar sticks to these cells and gives us an idea of how much sugar has been around for the preceding three months. In most labs, the normal range is 4-5.9 %. In poorly controlled diabetes, its 8.0% or above, and in well controlled patients it's less than 7.0%. The benefits of measuring A1c is that is gives a more reasonable view of what's happening over the course of time (3 months), and the value does not bounce as much as finger stick blood sugar measurements.

A nondiabetic person will have an A1c between 4% and 6%. The closer a diabetic can keep their A1c to 6% without experiencing excessive hypoglycemia, the better their diabetes is in control. As the A1c increases, so does the risk of complications.

While there are no guidelines to use A1c as a screening tool, it gives a physician a good idea that someone is diabetic if the value is elevated. Right now, it is used as a standard tool to determine blood sugar control in patients known to have diabetes.

The American Diabetes Association currently recommends an A1c goal of less than 7.0%, while other groups such as the American Association of Clinical Endocrinologists recommend a goal of less than 6.5%.

Of interest, studies have shown that there is a 10% decrease in relative risk for every 1% reduction in A1c. So, if a patients starts off with an A1c of 10.7 and drops to 8.2, though there are not yet at goal, they have managed to decrease their risk of microvascular complications by about 20%. The closer to normal the A1c, the lower the absolute risk for microvascular complications.

The A1c test and eAG calculation are used primarily to monitor the glucose control of diabetics over time. The goal of those with diabetes is to keep their blood glucose levels as close to normal as possible. This helps to minimize the complications caused by chronically elevated glucose levels, such as progressive damage to body organs like the kidneys, eyes, cardiovascular system, and nerves. The A1c test and eAG result give a picture of the average amount of glucose in the blood over the last few months. They can help you and your doctor know if the measures you are taking to control your diabetes are successful or need to be adjusted.
The A1c test is frequently used to help newly diagnosed diabetics determine how elevated their uncontrolled blood glucose levels have been. It may be ordered several times while control is being achieved, and then several times a year to verify that good control is being maintained.

Also called:
Hemoglobin A1c; HbA1c; Glycohemoglobin; Glycated hemoglobin; Glycosylated hemoglobin

Depending on the type of diabetes that you have, how well your diabetes is controlled, and your doctor, your A1c may be measured 2 to 4 times each year. The American Diabetes Association recommends testing your A1c at least twice a year. When someone is first diagnosed with diabetes or if control is not good, A1c may be ordered more frequently.

What does the test result mean?
A1c is currently reported as a percentage, and it is recommended that diabetics aim to keep their A1c below 7%. The report for your A1c test also may include an estimated Average Glucose (eAG), which is a calculated result based on your A1c levels. The purpose of reporting eAG is to help you relate your A1c results to your everyday glucose monitoring levels. The formula for eAG converts percentage A1c to units of mg/dL or mmol/L so that you can compare it to your glucose levels from home monitoring systems or laboratory tests.

It should be noted that the eAG is still an evaluation of your glucose over the last couple of months. It will not match up exactly to any one daily glucose test result. The American Diabetes Association has adopted this calculation and provides a calculator and information on the eAG on their web site.

The A1c test will not reflect temporary, acute blood glucose increases or decreases. Glucose swings will not be reflected in the A1c.
If you have a hemoglobin variant, such as sickle cell hemoglobin (hemoglobin S), you will have a decreased amount of hemoglobin A. This may limit the usefulness of the A1c test in monitoring your diabetes. If you have anemia, hemolysis, or heavy bleeding, your test results may be falsely low. If you are iron deficient, you may have an increased A1c measurement. If you have had a recent transfusion, then your A1c will be falsely increased (blood preservative solutions contain high glucose levels) and not accurately reflect your glucose control for 2 to 3 months.


How estimated Average Glucose (eAG) calculated
The ADAG formula that is used to calculate the eAG from your A1c result is:
28.7 X A1c – 46.7 = eAG

An example of this is an A1c of 6%. The calculation for this would be:

    28.7 X 6 – 46.7 = 126 mg/dl

for an estimated average glucose of 126 mg/dl.

What this means is that for every one percent that your A1c goes up, it is equivalent to your average glucose going up by about 29 mg/dl.

There is a correlation between A1c levels and average blood sugar levels as follows:


Mean blood sugar (mg/dl)


Home test for A1c.
There are FDA-approved tests that can be used at home including the Bayer A1C Now test.
The tests you do at home show your blood sugar level at that moment. The A1C test shows your average blood sugar level over the past two or three months. It's the best way to see how well your type 2 diabetes is controlled.

It usually takes two to three months to see changes in your A1C. So, you may get this test two to four times a year, depending on how well your treatment is working. The A1C blood test is usually done at your doctor's office.

The A1c test has the advantages of not requiring a person to be fasting and of giving an estimate of glucose levels for the past couple of months. There are, however, conditions such as anemia or the presence of hemoglobin variants that can interfere with the test’s interpretation. And there are currently no established cutoff values to compare A1c test results to in order to use them for diabetes screening or diagnosis.

Test Standarization
For more than a decade, a variety of national and international organizations have been working together as part of the National Glycohemoglobin Standardization Program and/or as part of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Included in the recent consensus statement of the ADA, IFCC, European Association for the Study of Diabetes, and the International Diabetes Federation were statements regarding a new way of reporting (see What does the test result mean?) and a statement recommending that a new improved reference system developed by the IFCC be adopted as the only valid “anchor” for measurement standardization. In the past, A1c tests have used different methods that have measured one or more of the glycated subcomponents of hemoglobin A. The result of this was an A1c test result that could vary significantly depending upon which method was used. The IFCC method measures only hemoglobin A1c.
The process of using the IFCC method will be invisible for people having an A1c test performed. The NGSP is in the process of certifying that manufacturers’ are capable of producing the same results as the IFCC system. Practically, as this is adopted over the next few years, it means that a person would get the same or very similar A1c results regardless of to which laboratory their test was sent.

An A1C higher than 7% is a warning sign that your diabetes is out of control and may increase your risk of developing complications1. If your A1C is high, your healthcare team may change your diabetes plan to help control your blood sugar better. Changes in your plan are expected from time to time and will help bring your A1C closer to normal. When your A1C is closer to normal (4-6%) you know that you are doing all you can to stay healthy. Research shows that good blood sugar control does lower your risk of developing major related health problems including heart disease, stroke, kidney disease, eye disease, nerve damage, amputations and circulation problems as mentioned earlier. By keeping your blood sugar close to normal, you can stop or delay the damage high blood sugar does to blood vessels and nerves.



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