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The A1C Test for Diabetes

Every three to six months, your internist or general practitioner may request a blood sugar test called a hemoglobin A1C test—also known as the HbA1C, glycohemoglobin, glycosylated hemoglobin, or glycated hemoglobin test. This test shows how well you have been managing your blood sugar for the six to 12-week period prior to your test.

You will still continue your at-home blood sugar testing, but this will help show your doctor if your plan is effective, or if you all need to rework your diabetes management.

What is Hemoglobin?

Hemoglobin is a substance within your red blood cells that carries oxygen through your body. If your diabetes is not controlled well, excess sugar will build up on the hemoglobin over time. Coated hemoglobin is called "glycated." An A1C test measures how much glycated hemoglobin is in your blood. The more glycated hemoglobin present in your blood, the more out of control your diabetes has been in recent weeks, and the poorer your control. The higher the A1C level, the higher your risk of developing complications from diabetes.

Why Have an A1C Test?

Your doctor will use an A1C test to make an initial diabetes diagnosis—this establishes a baseline A1C level for the future—and he will use it to monitor your diabetes and see how your treatment plan is working.

For those who have had diabetes for several years, consider an A1C test a maintenance test—to make sure you don’t require a change to your plan.  The A1C test gives you a months-long reading of your blood sugar level.

How often should I be tested?

This depends on the type of diabetes you have, your treatment plan, and how well you’ve previously managed your blood sugar levels.

  • If you have type 1 diabetes, you will likely be tested more frequently—as much as four or more times a year.
  • If you have type 2 diabetes, don’t use insulin, and have a history of keeping your blood sugar level within the healthy range, your doctor may only ask to test your blood twice a year.
  • If you have type 2 diabetes, use insulin, and have had trouble in the past with keeping your blood sugar within the healthy target range, your doctor may ask to test your hemoglobin four or more times a year.

What results should you expect?

For people who don’t have diabetes, the upper limit of normal for HbA1c is 5.6 percent. The goal for people with diabetes is individualized, with the gial determined between patient and healthcare provider. In general, the higher the A1C, the greater the risks of developing complications related to diabetes. 

If you are taking the A1C test to diagnose diabetes, two consecutive A1C readings over 6.5 percent are an indication of diabetes. An A1C reading between 5.7 and 6.4 percent is indicative of prediabetes—this means you are at risk for developing diabetes if you do not take steps to prevent it.

When an A1C test won’t work

The effectiveness of an A1C test may be limited in certain cases. Here are a few:

  • If you are anemic or have low levels of iron in your blood, your A1C test may return falsely high percentages.
  • If you experience heavy or chronic bleeding (possibly from your menstrual cycle), you may have an unusually low amount of hemoglobin. This will likely return a falsely low percentage for your A1C test.
  • If your hemoglobin has a variant—meaning you have an uncommon form of hemoglobin—your A1C test may be false. A hemoglobin variant can be confirmed by a lab test, but your future A1C tests will need to be read by a specialized lab that is equipped to test your particular hemoglobin variant.

Content licensed from:

Written by: Kimberly Holland
Medically reviewed on: Jun 17, 2014: Jason Baker, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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