Types of blood glucose tests
There are several different blood glucose tests, used to both diagnose diabetes as well as help individuals track and manage their blood sugars. But, what are these tests and what do they involve? Here is an overview of different blood glucose tests.
Four types of blood glucose tests
Hemoglobin A1C. This test provides an overview of your blood sugar (glucose) level over a three-month timespan. You don't have to fast before this test, which makes it very convenient. You simply go to a lab, where a technician draws a vial of blood. An A1c level of 6.5 or greater indicates you may have diabetes. An A1c level of 5.7 to 6.4 indicates pre-diabetes.
If your A1c level is higher than 5.7, you can expect to have the test performed every three months. It's important to note that the hemoglobin A1c test can give a false positive result in some individuals, including those with sickle cell anemia or thalassemia. Be sure to discuss the possibility of a false positive result with your doctor if you're of African, Mediterranean or Southeast Asian descent because you could have a hemoglobin variant that interferes with the accuracy of the A1c test.
Fasting Blood Glucose (formerly called 'Fasting Blood Sugar' or FBS). As the name implies, you need to have this blood draw performed on an empty stomach. It traditionally requires two fasting blood glucose tests before making a diagnosis of diabetes. Normal fasting blood sugar values are considered to be under 100 mg/dL. Two results over 126 mg/dL indicate you have diabetes. If your results fall between 100 and 125 mg/dL, your doctor may diagnose you with pre-diabetes and send you for a hemoglobin A1c test to confirm a diagnosis.
Random or casual blood glucose. This test is performed via blood draw at the lab when you're not fasting. It gives a glimpse into how your body handles the increased blood sugar levels triggered by eating. In general, a random blood glucose test result over 200 mg/dL may indicate diabetes. However, your doctor also takes into account whether or not you meet the risk factors for diabetes and whether or not you're experiencing symptoms.
Glucose tolerance test (GTT). While this test formerly was used to diagnose diabetes in the general population, it's now used mainly to screen pregnant women for a condition called gestational diabetes.
Think you have diabetes? Should you get a blood glucose test?
"There are three ways you can be diagnosed with diabetes, essentially," says Nora Saul, Certified Diabetes Educator and Nutrition Manager at Harvard University's Joslin Diabetes Center. "All of them involve some type of blood glucose test."
If you exhibit any symptoms of diabetes, such as excessive thirst or urination, or if you're in a high-risk category (obese, sedentary or of African-American, Hispanic/Latino or American Indian descent), you should ask your doctor about getting a glucose test at your annual physical. Together, you can decide which of these diagnostic tests is right for you.
Interview with Nora Saul, RD of Harvard University
CDC, 2011 National Diabetes Fact Sheet
National Institutes of Health, "Diagnosis of Diabetes"