What is HbA1c?
Hemoglobin A1c (HbA1c) is glycated hemoglobin, which basically means hemoglobin with some sugar (glucose) attached.
Hemoglobin is a protein within red blood cells that carries oxygen around the body. Blood glucose naturally attaches to this hemoglobin, so the more glucose in the blood, the more HbA1c will form.
Red blood cells survive for about 8-12 weeks. This means that HbA1c levels provide a good reflection of average blood glucose levels over that timeframe (1).
HbA1c tests can:
- Identify people with prediabetes (slightly elevated blood sugar and an increased risk of diabetes)
- Diagnose diabetes
- Monitor how well diabetes treatment is working in diabetics (2)
Why is an HbA1c test more informative than a blood glucose test?
Blood glucose tests are simple and many diabetics have home blood glucose monitors. However, blood glucose levels fluctuate, so a blood glucose test just measures the concentration of glucose at only the timepoint at which the blood sample was collected.
In contrast, an HbA1c test provides an average blood glucose level for the preceding 2-3 months (lifetime of the red blood cells). This provides a better understanding of where your blood glucose levels are at over an extended period.
HbA1c tests also have the distinct advantage of not requiring fasting. Often a blood glucose test taken at a doctor’s office requires a period of fasting (8-12 hours) prior to sample collection (3).
Why should I take an HbA1c test?
The CDC recommends people over the age of 45 should get screened for diabetes and prediabetes. An HbA1c test is the most informative and convenient test for this screening. People who have normal HbA1c values (<5.7%) usually don’t need to be screened again for three years, while those with prediabetes levels (5.7-6.4%) should be tested again in 1-2 years (4).
People under 45 years with certain risk factors may also need to take an HbA1c test. These risk factors include being overweight or obese, high blood pressure, history of heart disease, and physical inactivity (4).
HbA1c testing for diabetics
Individuals who have been diagnosed with type 2 diabetes (HbA1c level of 6.5% or higher) should use HbA1c tests to monitor the control of their blood glucose levels and ensure that they are attaining the recommended goal of <7.0% for diabetic adults. For well-controlled diabetes, HbA1c testing may only be required once or twice a year, while more frequent testing may be needed for other diabetics (4).
Higher HbA1c levels are associated with an increased risk of diabetic health complications, such as retinopathy, heart failure, and peripheral vascular disease (5). Higher levels of HbA1c are also associated with an increased risk of peripheral arterial disease, even among patients without diabetes (6).
Are there times when an HbA1c test is not useful?
Yes, there are various factors that may lead to misleading %HbA1c results, including diseases that affect hemoglobin (e.g. anemia), specific supplements (e.g. vitamins C and E), pregnancy, significant blood loss, high cholesterol, kidney, and liver disease (1). Alternative blood glucose testing methods may be required in those patients.
How can I lower my blood glucose?
A combination of diet, exercise, and medication can lower blood glucose levels and hence lower HbA1c levels. Several studies, including the Diabetes Control and Complications Trial (7), have demonstrated that improving HbA1c by 1% for people with diabetes reduces the risk of microvascular complications by 25%. More information about lowering high blood glucose is available here.
1. Hemoglobin A1C (HbA2c) Test. MedlinePlus. (Updated August 2021)
2. Understanding A1C. American Diabetes Association.
3. Fonseca V, Inzucchi SE, Ferrannini E. (2009). Redefining the diagnosis of diabetes using glycated hemoglobin. Diabetes Care. 32(7), 1344- 1345.
4. All About Your A1C. CDC. (Reviewed August 2021)
5. Eeg-Olofsson K, et al. (2010). New aspects of HbA1c as a risk factor for cardiovascular diseases in type 2 diabetes: an observational study from the Swedish National Diabetes Register (NDR). J Int Med. 268(5), 471-482.
6. Muntner O, et al. (2005). Relationship Between HbA1c Level and Peripheral Arterial Disease. Diabetes Care. 28(8), 1981-1987.
7. The Diabetes Control and Complications Trial Research Group. (1993). The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 329(14), 977–986.