When a person is suspected of having type 2 diabetes, there are several different types of blood tests that may be used to diagnose the disease, including the fasting glucose test, the oral glucose tolerance test, and the random glucose test. Of these, the fasting glucose test is the preferred method because it is highly accurate and simple to perform.
This section provides information on commonly used tests to diagnose type 2 diabetes. Only your doctor or healthcare professional can determine if you have type 2 diabetes.
Fasting Glucose Test
Diabetes is most often diagnosed using a fasting glucose test. For this test, you will be asked to go without eating for 10 to 16 hours, usually overnight, before a blood sample is drawn. The test will measure the amount of glucose in your blood. If your glucose level is equal to or greater than 126 milligrams per deciliter (mg/dL) on two or more fasting glucose tests performed on different days, you have type 2 diabetes.
This chart shows how the fasting glucose test is interpreted.
| If your fasting glucose level is: | This is what it means: |
| Less than 110 mg/dL | This is a normal fasting glucose level. |
| Less than 110 mg/dL, but you have symptoms of type 2 diabetes
OR Between 110 mg/dL and 126 mg/dL |
Although you do not have type 2 diabetes, these levels may indicate a condition known as impaired fasting glucose. Your healthcare professional may recommend another test to confirm this, usually an oral glucose tolerance test or a glycosylated hemoglobin test. |
| 126 mg/dL or more | You may have type 2 diabetes. Your healthcare professional will repeat the test another day to confirm. |
Oral Glucose Tolerance Test
In some instances, an oral glucose tolerance test may be performed to diagnose type 2 diabetes. When taking this test, you will usually be asked to eat a diet that is high in carbohydrates for 3 days. Before the test, you will have to fast for 10 to 16 hours, usually overnight. When you go to the office or laboratory, you will first have a fasting blood sample drawn. You will then be asked to drink a sweet liquid that contains glucose. Samples of your blood will be taken 5 times over a period of 3 hours. Your doctor or healthcare professional will give you specific instructions prior to having a glucose tolerance test.
In a person who does not have type 2 diabetes, the glucose (sugar) levels in the blood will rise and then fall quickly. In someone with type 2 diabetes, blood glucose levels will often rise higher than normal and will not drop as fast. If your blood sugar level is above 200 mg/dL at 2 hours, you may have diabetes. Your doctor or healthcare professional will either repeat the test or perform a fasting glucose test on a different day to confirm the diagnosis.
After an oral glucose tolerance test, if the blood glucose levels are somewhere between those of a person without type 2 diabetes and a person with type 2 diabetes, a person is said to have impaired glucose tolerance. Although people with this condition may not have type 2 diabetes, they are at increased risk of developing it. If you have impaired glucose tolerance, your doctor or healthcare professional may recommend that you lose weight and exercise to help manage your risk of developing type 2 diabetes.
This chart shows how the oral glucose tolerance test is interpreted.
| If your glucose level is: | This is what it means: |
| Less than 140 mg/dL at 2 hours | This is normal. |
| Between 140 mg/dL and 200 mg/dL at the end of the test | You may have impaired glucose tolerance. |
| Greater than 200 mg/dL at 2 hours | You may have type 2 diabetes. Your healthcare professional will repeat the test on another day or perform a fasting to confirm. |
Random Glucose Test
When symptoms of diabetes are present, a blood sample that is taken in a non-fasting state (otherwise known as a random blood sample) may be used to test for type 2 diabetes. In this case, a glucose (sugar) level of greater than 200 mg/dL accompanied by symptoms of hyperglycemia suggests a person may have type 2 diabetes. However, the result must be confirmed on another day by performing a fasting glucose test or an oral glucose tolerance test.
If you have been diagnosed with type 2 diabetes and diet and exercise no longer control your blood sugar, treatments are available that may help you lower your blood sugar levels. One such treatment is Glucophage XR. Ask your doctor or healthcare professional if Glucophage XR is right for you.