Glycated hemoglobin
Over time, the hemoglobin in red blood cells tends to bind to glucose, the blood sugar. The amount of glucose-bound hemoglobin depends on blood glucose levels. In diabetics with high blood glucose levels, a larger percentage of hemoglobin will bind to glucose. The glycated hemoglobin or HbA1c test measures quantities of sugar attached to the hemoglobin in red blood cells.
| What is the purpose of this test? | A HbA1c test may be requested as part of a routine examination, particularly in people at high risk of developing diabetes. The HbA1c test is used for:
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| How to prepare? |
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| Associated tests | Related tests include the following:
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| How it is done? | A small blood sample is drawn, usually from a vein in the arm. |
| How long before I get the results? | Results are usually ready within a day. It may take longer to receive your results. |
Various tests can be performed to detect diabetes. Typical blood tests include fasting blood sugar, glycated hemoglobin and Oral glucose tolerance test (OGTT). Random blood sugar testing may also be used. Normally, two blood tests with abnormal results are needed to establish a diagnosis of diabetes.
| 4.8-5.9% | Normal |
| 6.0-6.4 % | Prediabetes |
| ≥ 6.5% | Diabetes |
In order to delay and even prevent the complications of diabetes, target values for glycated hemoglobin and blood sugar have been developed. These targets must be assessed for each individual diabetic, depending on a number of factors (e.g. age, sex, health condition). The following table shows target values for glycated hemoglobin for adults with diabetes.
| ≤ 6.5% | In people with type 2 diabetes, to reduce the risk of chronic kidney disease and retinopathy in the presence of a low risk of hypoglycemia. |
| ≤ 7.0% | In most people with type 1 or type 2 diabetes. |
| 7.1-8.5% | In some people with type 1 or type 2 diabetes, such as those:
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The HbA1c levels reflect the blood glucose levels of the last 2 to 3 months. In persons with diabetes, it is possible to correlate between HbA1c levels and the estimated mean blood glucose level. In the following table are some correspondences between HbA1c test results and the associated estimated mean blood glucose level.
| HbA1c (%) | Estimated mean blood sugar (mmol/L) | HbA1c (%) | Estimated mean blood sugar (mmol/L) |
|---|---|---|---|
| 5 | 5.4 | 10 | 13.3 |
| 5.5 | 6.2 | 10.5 | 14.2 |
| 6 | 6.9 | 11 | 14.9 |
| 6.5 | 7.7 | 11.5 | 15.7 |
| 7 | 8.6 | 12 | 16.6 |
| 7.5 | 9.4 | 12.5 | 17.3 |
| 8 | 10.2 | 13 | 18.1 |
| 8.5 | 10.9 | 13.5 | 18.9 |
| 9 | 11.8 | 14 | 19.7 |
| 9.5 | 12.6 |
What does an abnormal test result mean?
High values of HbA1c:
- High blood glucose levels over the last 2 to 3 months
- Presence of prediabetes or diabetes
- Sub-optimal control of the disease in a person with diabetes
Low values of HbA1c:
- Episodes of hypoglycemia (low blood sugar) in the past 2 to 3 months.
Factors that can interfere with test accuracy
Factors that can interfere with HbA1c test results, mainly due to their impact on the red blood cells, include the following:
- Spleen removal or damage
- Certain types of anemia
- Pregnancy
- Alcohol use disorder
- Blood transfusion
- Kidney or liver damage
- Hemorrhage (bleeding)
- Living at high altitudes
- Vitamin B12 deficiency
What you should know before going for this test
When you go in for a blood test or any other medical exam, it's always a good idea to bring a complete list of any prescriptions, over-the-counter medications, or natural health products you're taking. Unless otherwise advised, it's best to take your medications as usual on blood test days. If in doubt, don't hesitate to talk to your healthcare professional.
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The patient information leaflets are provided by Vigilance Santé Inc. This content is for information purposes only and does not in any manner whatsoever replace the opinion or advice of your health care professional. Always consult a health care professional before making a decision about your medication or treatment.