The HbA1c shows if your blood glucose has been close to normal or high during the past three to four months. If blood glucose levels are elevated, then the HbA1c will be elevated. Since it is impossible to test blood glucose levels at all times throughout the day, the HbA1c is helpful. Testing with a meter measures the actual level of glucose in your blood at that exact time. The HbA1c test looks at the bigger picture; it measures your overall control for the past three to four months.
The HbA1c measures the amount of sugar attached to a protein, hemoglobin, that is found in the red blood cell. Once attached, it stays there for 90 to 120 days - the life of the red blood cell.
In Canada, blood glucose levels are measured in mmol/L, and the HbA1C is measured in a percentage. Look at the comparisons between blood glucose levels and the HbA1C. (These comparisons are taken from the 1998 CDA Clinical Practice Guidelines.)
Two large studies have been done on preventing diabetes complications: the DCCT (Diabetes Control and Complications Trial 1993) and the UKPDS (United Kingdom Prospective Diabetes Study Group 1998). Both studies show that good blood glucose control and reducing the HbA1c (even by one per cent) reduces the risk of complications associated with diabetes. Studies like these recommend that you maintain your HbA1c at less than seven per cent (<7.0%).
Many people with diabetes test their blood glucose levels only once a day. The most common testing time is before breakfast, also known as the fasting blood glucose (fbs) or fasting plasma glucose (fpg). If someone's blood glucose levels are within the optimal range of four to seven (4.0 to 7.0) mmol/L, but their HbA1c is greater than eight per cent (>8.0%), we know that their blood glucose levels are elevated at a time of the day other than before breakfast.
Now it is time to try to locate the highs; most of the highs are after meals. Testing after meals is generally done one to two hours after eating. Then we need to focus on lowering the after-meal test results to improve the HbA1c. Research suggests that post-meal test results may have the greatest benefit for the HbA1c. Talking with your nurse educator, dietitian or doctor is often helpful at this point. You may need to make changes to your meals, activity or medications.
|FASTING OR PRE-MEAL GLUCOSE LEVEL||GLUCOSE LEVEL 1-2 HOURS AFTER MEAL||HBA1C|
|Ideal Control||3.8 - 6.1 mmol/L||4.4 - 7.0 mmol/L||4.0 - 6.0%|
|Optimal Control||4.0 - 7.0 mmol/L||5.0 - 11.0 mmol/L||< 7.0%|
|Suboptimal Control||7.1 - 10.0 mmol/L||11.1 - 14.0 mmol/L||7.0 - 8.4%|
|Inadequate Control||> .10.0 mmol/L||> 14.0 mmol/L||> 8.4%|
The Canadian Diabetes Association recommends the test be repeated every three to four months. If blood glucose levels are within your goal range when testing throughout the day and your HbA1c also reflects these goals, then decreasing the frequency of the test may be acceptable.
If your control is outside of your goal range or you have been making changes to the treatment plan, testing your HbA1c every four months is suggested. One of the best uses of an HbA1c is to see how it changes over time. It is always best to discuss frequency of tests with your diabetes educator or doctor.
Work with your diabetes educator and doctor to determine your blood glucose goals. Ask for more information on diabetes tests and preventing complications associated with diabetes. By using the information available, you can stay healthy with diabetes.