Your doctor will perform tests to confirm if you have diabetes. These tests are used for diagnosis:
- A fasting plasma glucose test measures your blood glucose after you have gone at least 8 hours without eating. This test is used to detect diabetes or pre-diabetes.
- An oral glucose tolerance test measures your blood glucose after you have gone at least 8 hours without eating and 2 hours after you drink a glucose-containing beverage. This test can be used to diagnose diabetes or pre-diabetes.
- In a random plasma glucose test, your doctor checks your blood glucose without regard to when you ate your last meal. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.
Positive test results are confirmed by your doctor, by repeating the fasting plasma glucose test or the oral glucose tolerance test on a different day.
Because of ease of use, acceptability to patients and lower cost, the FPG is the preferred diagnostic test. Fasting is defined as no caloric intake for at least 8 hours.
- If your fasting glucose level is 100 to 125 mg/dL, you have a form of pre-diabetes called impaired fasting glucose (IFG), meaning that you are somewhat more likely to develop type 2 diabetes but do not have it yet.
- A level of 126 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.
The OGTT requires you to fast for at least eight hours before the test. Your plasma glucose is measured immediately before, at intermediate times, and two hours after you drink a liquid containing 75 grams of glucose dissolved in water.
- If your blood glucose level is between 140 and 199 mg/dL two hours after drinking the liquid, you have a form of pre-diabetes called impaired glucose tolerance or IGT, meaning that you are more likely to develop type 2 diabetes but do not have it yet.
- A two-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.
A random blood glucose level of 200 mg/dL or more, plus presence of the following symptoms, can mean that you have diabetes:
- increased urination
- increased thirst
- unexplained weight loss
Other diabetes symptoms include fatigue, blurred vision, increased hunger, and sores that do not heal. Your doctor will check your blood glucose level on another day using the FPG or the OGTT to confirm the diagnosis.
Source: NIDDK, National Institutes of Health website.