A glycohemoglobin test is a blood test used primarily to monitor diabetes. It measures a patient’s average glucose (blood sugar) level over the past two to three months.

Along with other glucose tests, glycohemoglobin (GHb) tests can indicate how well a patient’s diabetes has been controlled and whether the average blood glucose level is too high. The test can also verify self-testing results and blood test results from a physician, determine the effectiveness of a diabetes management plan and predict a patient’s risk of developing complications.

Many physicians refer to a glycohemoglobin test simply as an A1C test. This is actually the most common type of glycohemoglobin test ordered by physicians. Traditionally requiring laboratory analysis, glycohemoglobin tests can now be performed in a doctor’s office or even at home with results available within minutes.

Glycohemoglobin, or glycosylated hemoglobin, is a term used for glucose that has glycated (bonded) with hemoglobin, the part of the blood that carries oxygen to the cells of the body. High levels of glycosylated hemoglobin are proportional to high blood glucose (hyperglycemia). Excess glucose can damage the nerves, blood vessels, heart, kidneys, eyes and other organs.

Once glucose attaches itself to hemoglobin, it remains there for the life of the red blood cell, about 120 days. As a result, the evidence of high glucose is still detectable as glycosylated hemoglobin, even after blood glucose levels have returned to normal. Whereas most other glucose tests provide a “snapshot” of the amount of glucose in a person’s blood at any one time, glycohemoglobin tests provide more of an indirect measurement of glucose levels for the past few months.

Most people with diabetes require a glycohemoglobin test two to four times a year. Changes in diet, activity or daily medications are not required before testing.