All about A1c (Part 2)

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1. A1c can give false results in some people. It can be unreliable for diagnosing or monitoring diabetes in people with certain conditions that are known to interfere with the results. Interference should be suspected when A1c results seem very different from the results of a blood glucose test. People of African, Mediterranean, or Southeast Asian descent, or people with family members with sickle cell anemia or a thalassemia are particularly at risk of interference. People in these groups may have a less common type of hemoglobin, known as a hemoglobin variant that can interfere with some A1c tests. Most people with a hemoglobin variant have no symptoms and may not know that they carry this type of hemoglobin.
2. Not all of the A1c tests are unreliable for people with a hemoglobin variant. People with false results from one type of A1c test may need a different type of A1c test for measuring their average blood glucose level.
3. False A1c results may also occur in people with other problems that affect their blood or hemoglobin. For example, a falsely low A1c result can occur in people with anemia, heavy bleeding.
4. A falsely elevated A1c result can occur in people who are very low in iron, for example, those with iron deficiency anemia.
5. Other causes of abnormal A1c results include kidney failure and liver disease
6. Health care providers can use the A1c test to monitor blood glucose levels in people with type 1 or
type 2 diabetes. The A1c test is not used to monitor gestational diabetes.
7. The American Diabetes Association (ADA) recommends that people with diabetes who are meeting treatment goals and have stable blood glucose levels should have the A1c test twice a year. Health care providers may repeat the A1c test as often as four times a year until blood glucose levels reach recommended levels.
8. The A1c test helps health care providers adjust medication to reduce the risk of long-term diabetes complications. Studies have demonstrated substantial reductions in long-term complications with the lowering of A1c levels.
9. When the A1c test is used for monitoring blood glucose levels in a person with diabetes, the blood sample can be analyzed in a health care provider’s office using a POC test to give immediate results. However, POC tests are less reliable and not as accurate as most laboratory tests.
10. Estimated average glucose (eAG) is calculated from the A1c. It helps people with diabetes relate their A1c to daily glucose monitoring levels. The eAG calculation converts the A1c percentage to the same units used by home glucose meters i.e. milligrams per deciliter (mg/dL). The eAG number will not match daily glucose readings because it is a long-term average rather than the blood glucose level at a single time, as measured with the home glucose meter. (Diabetes Care 2011;34(Supp 1):S11–S61, Table 9)

A1c (%) eAG (mg/dL)
6 126
7 154
8 183
9 212
10 240
11 269
12 298

11. People will have different A1c targets depending on their diabetes history and their general health.
12. Studies have shown that people with diabetes can reduce the risk of diabetes complications by keeping A1c levels below 7%.
13. An A1c level that is safe for one person may not be safe for another. For example, keeping an A1c level below 7% may not be safe if it leads to problems with hypoglycemia.
14. Less strict blood glucose control, or an A1c between 7-8 % or even higher in some circumstances, may be appropriate in people who have limited life-expectancy; long-standing diabetes and difficulty attaining a lower goal; severe hypoglycemia and advanced diabetes complications such as chronic kidney disease, nerve problems, or cardiovascular disease
15. Large changes in a person’s blood glucose levels over the past month will show up in their A1c test result, but the A1c does not show sudden, temporary increases or decreases in blood glucose levels. Even though the A1c represents a long-term average, blood glucose levels within the past 30 days have a greater effect on the A1c reading than those in previous months.

All about A1C (Part 1)

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1. A1c is a blood test that provides information about a person’s average levels of blood glucose over the past 3 months. It is also called the hemoglobin A1c, HbA1c or glycohemoglobin test.

2. The A1c test is based on the attachment of glucose to hemoglobin, the protein in red blood cells (RBCs) that carries oxygen. In the body, RBCs are constantly forming and dying, but typically they live for about 3 months. Thus, the A1c test reflects the average of a person’s blood glucose levels over the past 3 months. The result is reported as a percentage. The higher the percentage, the higher a person’s blood glucose levels have been. A normal A1c level is below 5.7%.

3. In 2009, an international expert committee recommended the A1c test as one of the tests available to help diagnose type 2 diabetes and pre-diabetes. Previously, only the traditional blood glucose tests were used to diagnose diabetes and pre-diabetes.

4. Because the A1c test does not require fasting and blood can be drawn for the test at any time of day, experts are hoping its convenience will allow more people to get tested thus, decreasing the number of people with undiagnosed diabetes.

5. AIc testing is important because early in the disease diabetes has no symptoms. Testing enables health care providers to find and treat diabetes before complications occur and to find and treat pre-diabetes, which can delay or prevent type 2 diabetes from developing.

6. No test is perfect, the A1c and blood glucose tests are the best tools available to diagnose diabetes, a serious and life-long disease.

7. A1c laboratory tests are now standardized. Earlier, the A1c test was not recommended for diagnosis of type 2 diabetes and pre-diabetes because the many different types of A1c tests could give varied results. The accuracy has been improved by the National Glycohemoglobin Standardization Program (NGSP), which developed standards for the A1c tests. The NGSP certifies that manufacturers of A1c tests provide tests that are consistent with those used in a major diabetes study. The study established current A1c goals for blood glucose control that can reduce the occurrence of diabetes complications, such as blindness and blood vessel disease. (Nathan DM, Genuth S, Lachin J, et al. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. New England Journal of Medicine 1993:329(14)977–86).

8. When the A1c test is used for diagnosis, the blood sample must be sent to a laboratory that uses an NGSP-certified method for analysis to ensure the results are standardized. Blood samples analyzed in a health care provider’s office, known as point-of-care (POC) tests, are not standardized for diagnosing diabetes. The following table provides the percentages that indicate diagnoses of normal, diabetes, and pre-diabetes according to A1c levels.

Diagnosis* A1c Level
Normal < 5.7%
Diabetes ≥ 6.5%
Pre-diabetes 5.7 – 6.4%
*Any test for diagnosis of diabetes requires confirmation with a second measurement unless there are clear symptoms of diabetes.

9. Having pre-diabetes is a risk factor for getting type 2 diabetes. People with pre-diabetes may be retested each year. Within the pre-diabetes A1c range of 5.7-6.4%, the higher the A1c, the greater the risk of diabetes. Those with pre-diabetes are likely to develop type 2 diabetes within 10 years, but they can take steps to prevent or delay diabetes.

10. A1c test may be used at the first visit to the health care provider during pregnancy to see if women with risk factors had undiagnosed diabetes before becoming pregnant. After that, the oral glucose tolerance test (OGTT) is used to test for diabetes that develops during pregnancy—known as gestational diabetes. After delivery, women who had gestational diabetes should be tested for persistent diabetes. Blood glucose tests, rather than the A1c test, should be used for testing within 12 weeks of delivery.

11. The standard blood glucose tests used for diagnosing type 2 diabetes and pre-diabetes, the fasting plasma glucose (FPG) test and the OGTT, are still recommended. The random plasma glucose test, also called the casual glucose test, may be used for diagnosing diabetes when symptoms of diabetes are present. In some cases, the A1c test is used to help health care providers confirm the results of a blood glucose test.

12. In some people, a blood glucose test may indicate a diagnosis of diabetes while an A1c test does not. The reverse can also occur i.e. an A1c test may indicate a diagnosis of diabetes even though a blood glucose test does not. Because of these variations in test results, health care providers repeat tests before making a diagnosis. People with differing test results may be in an early stage of the disease, where blood glucose levels have not risen high enough to show on every test. Sometimes, making simple changes in lifestyle—losing a small amount of weight and increasing physical activity—can help people in this early stage reverse diabetes or delay its onset.
13. All laboratory test results can vary from day to day and from test to test. Results can vary.
a. Within the person being tested: A person’s blood glucose levels normally move up and down depending on meals, exercise, sickness, and stress.
b. Between different tests: Each test measures blood glucose levels in a different way. For example, the FPG test measures glucose that is floating free in the blood after fasting and only shows the blood glucose level at the time of the test. Repeated blood glucose tests, such as self-monitoring several times a day with a home meter, can record the natural variations of blood glucose levels during the day. The A1c test represents the amount of glucose attached to hemoglobin, so it reflects an average of all the blood glucose levels a person may experience over 3 months. The A1c test will not show day-to-day changes.

The following chart shows how multiple blood glucose measurements over 4 days compare with an A1c measurement.

Note: Blood glucose (mg/dL) measurements were taken four times per day (fasting or pre-breakfast, pre-lunch, pre-dinner, and bedtime). The straight black line indicates an A1c measurement of 7.0%. The blue line shows blood glucose test results from self-monitoring four times a day over a 4-day period.

c. Within the same test: Even when the same blood sample is repeatedly measured in the same laboratory, the results may vary due to small changes in temperature, equipment, or sample handling.

14. The A1c test result can be up to 0.5% higher or lower than the actual percentage. This means an A1c measured as 7.0% could indicate a true A1c anywhere in the range from 6.5-7.5%. The drawing below shows the range of variation that can occur when an A1C is 7.0% on the lab report.