- Measures glucose in blood cells |
- No fasting before test necessary |
- Shows levels between 2 to 3 months |
- Recent improvement may not reflect |
- Cannot be immediately altered by drugs |
- Incorrect readings are possible |
- Indicator of complication risk in diabetics |
- May show risk of diabetes or pre-diabetes |
- Danger of low levels in insulin users |
- eAG conversion gives average daily readings |
- Ask a Doctor
If you are a diabetic or have recently been diagnosed, then you will be familiar with the HbA1C test. It is one of the most effective methods of monitoring glucose control in diabetes management. Insurance companies may also request this test before covering a diabetic and there is good reason that it is the test of choice these days. It is not a snapshot of your blood glucose levels at the time of taking the blood sample. Rather it gives you an idea of your blood glucose levels over a period of a few months.
Measures glucose in blood cells
Most other glucose tests measure the amount of glucose circulating in your blood or being passed out in the urine at the time when the sample was collected. It can change within hours. However, an A1c measures the changes in your red blood cells that arises with high blood glucose levels. It measures what is known as glycated hemoglobin which is within red blood cells. Hemoglobin is the important compound in red blood cells that carries oxygen through the bloodstream. When the glucose levels are high, it combines with the hemoglobin over time to form glycated hemoglobin.
No fasting before test necessary
Eating or drinking before most glucose tests can affect the results. For this reason these tests are done early in the morning before a person has their first meal. However, fasting is not necessary for an HbA1c. It can be done anytime during the day, before or after a meal, and still give an accurate result. The HbA1c test indicates the glucose levels over weeks and months, and does not change over hours and days. Even drinking a sugary drink before the test will not affect the result. No other preparation is required prior to the test. Nevertheless it is important to follow your doctor’s orders.
Shows levels between 2 to 3 months
The effects of high glucose levels in the body, particularly its binding with hemoglobin, happens over a long period of time. The HbA1c measures this to assess your glucose levels over that period of time without relying solely on your own readings with a home glucose meter or other blood or urine glucose tests. Itt is done in a laboratory although the blood sample may be sometimes taken at a doctor’s office. The test is highly sensitive test which can indicate your average blood glucose levels over a 6 to 12 week period.
Recent improvement may not reflect
As mentioned, the effects of a high blood glucose level happens over time and this can be detected with an HbA1c. If you were not controlling your blood glucose levels for 2 to 3 months prior to the test, then it will reflect in the HbA1c. Even if you start controlling your glucose levels in the past week or two before the test, it may not help in reducing your HbA1c levels significantly. Continuing with this proper glucose control may show lower HbA1c levels in another 2 to 3 months but recent improvements will not reflect in the HbA1c test results.
Cannot be immediately altered by drugs
Taking antidiabetic medication before the HbA1c test, or even properly using these drugs weeks before the test, will not help reduce your HbA1c levels. Many diabetics do not practice proper glucose control through diet, lifestyle and with medication. They only make a concerted effort to do so just before they are to see their doctor for regular checkups. But an HbA1c can reflect that there was poor glucose control in the months prior even if other blood glucose tests indicate low readings at the time of seeing a doctor. Never take high dosages of diabetic medication in an attempt to alter your glucose readings. You could be risking your life and it will not work for the HbA1c test.
Incorrect readings are possible
While the HbA1c is one of the best indicators of glucose control for the past 2 to 3 months, it can at times be inaccurate. Your HbA1c test results may be inaccurate if you have:
- Sickle cell disease
- Anemia or recent heavy bleeding
- A recent blood transfusion
- High cholesterol levels
- Been taking large doses of vitamin C and E
- Kidney or liver disease
It is therefore important to tell your doctor if any of these conditions/situation are present or have occurred in the recent past. In this way your doctor can redo the test in the near future or conduct other tests to assess your glucose control.
Indicator of complication risk in diabetics
The long term goal of any diabetes management program is to delay the onset of diabetic complications and minimize the severity of these complications. The high blood glucose levels damages cells over times. Blood vessels and nerves in particular are adversely affected when the glucose levels remain high for long periods. Your HbA1c levels are an indicator of your risk with regards to these complications. If your HbA1c repeatedly indicates high readings then it means that you are at a greater risk of developing complications sooner. It also means that these complications may be more severe than in a diabetic who has lower HbA1c levels.
May show risk of diabetes or pre-diabetes
HbA1c levels are expressed as a percentage or as mmol/mol. Diabetics have levels of 6.5% (47 mmol/mol) or higher and people with normal glucose control (non-diabetics) should have levels below 5.7% (39 mmol/mol). However, HbA1 levels can also be useful for indicating the risk of developing diabetes later in life. People with levels of 5.7% to 6.4% (39 to 46 mmol/mol) are at an increased risk of becoming diabetic in the future. Pre-diabetes or impaired glucose tolerance is the term used to described a person who has glucose levels between that of a diabetic and a non-diabetic. A person can have pre-diabetes for a period of years before becoming diabetic. Prediabetes is reversible but diabetes is not.
Danger of low levels in insulin users
While diabetics have to aim for good glucose control and low HbA1c levels, sometimes low levels can indicate a problem. Insulin-dependent diabetics who have HbA1c levels lower than 6.2% need to be be especially cautious. These low levels may indicate episodes where the glucose levels dip too low. This is known as hypoglycemia. It is more likely to be serious in people who use insulin, particularly when their insulin dosage is incorrect. A person may become disorientated, unable to see properly or lose coordination. It can lead to fainting and even be fatal.
eAG conversion gives average daily readings
The HbA1c is a useful test to monitor your glucose control over a period of 2 to 3 months. Your doctor may want to run this test two or more times in a year. But what does it mean to you the diabetic who is testing your glucose levels with a home tester? The eAG (estimated Average Glucose) correlates the HbA1c reading with the average daily glucose levels in mg/dL or mol/L. It helps diabetics put the HbA1c levels in the context of the readings given by their home testing machines. It is solely meant to be a guide for diabetics. A HbA1C to eAG conversion calculator can be found on the American Diabetes Association (ADA) website.