Diabetes and Lipid Clinic of Alaska

 

 


About the glycohemoglobin test

The glycohemoglobin test (or A1C test) measures the amount of glycosylated hemoglobin in the blood. Hemoglobin is a protein component of red blood cells that transports oxygen to the cells in the body. Hemoglobin combines, or glycates, with glucose (blood sugar) to make glycosylatedhemoglobin. The glycohemoglobin test measures the amount of glycosylated hemoglobin, which is proportional to the amount of glucose in the blood.

Whereas glucose monitoring is a method of measuring day–to–day glucose control, a glycohemoglobin test can provide an overall view of how a diabetes management plan is working. The test measures a person’s average glucose control for the previous two to three months.

Patients are able to monitor their past glucose levels because once glucose attaches itself to hemoglobin, it remains there for the life of the red blood cell, about 120 days. So even after blood glucose levels have returned to normal, the evidence of high glucose is still detectable as glycosylated hemoglobin.

Glycohemoglobin levels are measured as a percentage of total hemoglobin. The average person has between 4 and 6 percent glycosylated hemoglobin. A diabetic individual with high blood glucose (hyperglycemia) will have a higher percentage. The amount depends on the person’s average blood glucose level for the weeks leading up to the test.

The American Diabetes Association (ADA) recommends that people with diabetes have a glycohemoglobin test when they are diagnosed or when they begin treatment. After the intitial test, additional glycohemoglobin tests should be conducted approximately every 4 months depending upon the discretion of the doctor.

All people with diabetes can benefit from a glycohemoglobin test. Benefits include:

  • Confirming other test results. Glycohemoglobin tests can verify self–testing results and blood test results from a physician.

  • Determining the effectiveness of a diabetes management plan. If results are above a patient’s target percentage, the physician can adjust the meal plan, exercise plan or medications.

  • Predicting the patient’s risk of developing complications. High glycosylated hemoglobin levels are equivalent to high blood glucose levels.  Hyperglycemia increases a person’s risk of developing complications, such as:
    • Kidney disease (diabetic nephropathy)
    • Nerve damage (diabetic neuropathy) 
    • Cardiovascular disorders (including heart disease, stroke and diabetic angiopathy)
    • Eye diseases (diabetic retinopathy, glaucoma, cataracts)
  • Encouraging the patient. Healthy test results can show people the effectiveness of their diet and exercise decisions.

Although glycohemoglobin tests can provide an idea of how well a patient’s diabetes management plan is working, there are disadvantages. Major drawbacks of solely using glycohemoglobin tests include:

  • Day–to–day glucose control is not measured. Patients must still rely on daily self–testing with a glucose meter to spot patterns of high and low glucose.

  • Insulin amounts cannot be adjusted based on glycohemoglobin test results. People with diabetes need daily results to adjust insulin doses and prevent low and high blood glucose.

  • Many factors can cause inaccurate results, including:
    • Diseases that affect hemoglobin such as anemia
    • Diseases of the liver and kidneys
    • Vitamins C and E
    • High levels of lipids
    • A blood transfusion or severe blood loss within three months of testing
    • Pregnancy

It is also important for patients to be aware that laboratories measure hemoglobin levels in different ways. As a result, normal values may vary slightly from lab to lab. However there is an effort to standardize the test so that all results are comparable to those of the Diabetes Control and Complications Trial (DCCT). Patients should be aware of the normal range for the lab their physician is using.

Types and differences of Glycohemoglobin tests

There is no special preparation for a glycohemoglobin test. The blood sample can be taken at anytime.

Traditionally, glycohemoglobin tests have been performed in laboratories. A blood sample would be taken in a physician’s office and the sample would be sent to a laboratory for analysis. However more options are now available.

Glycohemoglobin tests can now be performed in physician offices.

Some tests provide immediate results to the patient and physician. A physician can collect a drop of blood from a finger prick into a supplied capillary holder. Light pressure and sterile gauze are then applied to the puncture site to stop the bleeding. A bandage is usually not necessary. The sample is then inserted into a cartridge, and the cartridge is placed in an analyzer. Results are available in 6 minutes. The advantage is the patient can then discuss the results with the physician.

Treatments that may follow the test

A typical goal for people with diabetes, and one suggested by the U.S. National Institute of Diabetes and Digestive and Kidney Diseases, is a glycohemoglobin test result of less than 7 percent. A level of 7 percent means that 7 percent of the hemoglobin is combined with glucose (blood sugar). It also means that the average plasma blood glucose level for the previous two to three months was 170 mg/dL.

In September 2005, the International Diabetes Federation (IDF), which includes organizations in 150 nations, issued new guidelines urging that people with type 2 diabetes aim for a maximum glycohemoglobin result of 6.5 percent to reduce the risk of diabetic complications. However, the IDF acknowledged that most diabetic individuals fell short of this target. The American College of Endocrinology and the American Association of Clinicial Endocrinologists also recommend aiming for 6.5 percent or less. In 2005, though, they released a nationwide study of more than 157,000 people with type 2 diabetes that showed only one-third meeting this goal.

At the Diabetes and Lipid Clinic of Alaska, we prefer the glycohemoglobin test be less than 6% and occasionally in the 5% range. Caution must be taken to avoid hypoglycemia and this recommendation has to be individualized.
Patients can convert their glycohemoglobin test results as:

Glycohemoglobin
test results

Average plasma
blood glucose level

6 percent

135 mg/dL

7 percent

170 mg/dL

8 percent

205 mg/dL

9 percent

240 mg/dL

10 percent

275 mg/dL

11 percent

310 mg/dL

12 percent

345 mg/dL


When a patient’s test result is higher than the physician–recommended goal, the physician may make changes to the patient’s diabetes care plan. A change in treatment plan is usually recommended when results are higher than 8 percent. A physician may recommend changes in meal plan, exercise plan or medication. If changes are made, the patient may need to have glycosylated hemoglobin retested in three months to monitor the effectiveness of the new treatment.

A goal of 6.5 percent or 7 percent is not realistic or appropriate for everyone. Patients who are pregnant or trying to become pregnant may have a recommended target of closer to 6 percent, if they are not suffering from too many episodes of hypoglycemia (low blood glucose). Children under the age of 7, the elderly and people with certain health conditions may have goals higher than 7 percent to prevent hypoglycemia.

Patients are encouraged to lower their high glucose levels to prevent or delay the onset of diabetic complications. Research studies have shown that for every 1 percent reduction in glycohemoglobin test results, the risk of developing eye, kidney, nerve and blood vessel disease is significantly reduced.

Please consult with the physicians at the Diabetes and Lipid Clinic of Alaska for additional information.

Return to Top