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Diabetes & Heart Disease - Diabetes Testing

Who should be tested for diabetes?

Everyone 45 years or older should be tested for diabetes. People younger than 45 should be tested if they are overweight and have one or more risk factors for diabetes, particularly high blood pressure or high cholesterol. If your test results are normal, you should be tested again every 3 years. If you have prediabetes, you should be checked every 1 to 2 years after your diagnosis.


What is a fasting plasma glucose test?

A Fasting plasma glucose (FPG) test is the preferred test for diagnosing type 1 and type 2 diabetes. It is a simple blood test that measures blood sugar after you have fasted for at least 8 hours. Blood sugar is measured in milligrams (mg) per deciliter (dL) of blood. An FPG value of 126 mg/dL or greater means that you have diabetes. An FPG value of 110 mg/dL to 125 mg/dL means that you have prediabetes.

Fasting Plasma Glucose Level (mg/dL)6

Normal blood glucose

less than 110




126 or higher

What is a nonfasting blood glucose test?

A Nonfasting (casual) blood glucose test, used to diagnose type 1 or 2 diabetes, is done regardless of when you had your last meal. You will be diagnosed with diabetes if the casual level of sugar in your blood is 200 mg/dL or more and you have symptoms of diabetes.

What is an oral glucose tolerance test?

An oral glucose tolerance test (OGTT) measures the amount of sugar in your blood 2 hours after you drink a glucose syrup. This test can tell how well your body processes the sugar. You will be asked to follow a diet, containing at least 150 grams of carbohydrates per day, for 3 days before this test. Then you will fast for 8 hours immediately before the test. A blood sample is taken at the end of the fast, then again 1 to 3 hours after you drink the glucose syrup. This test can diagnose diabetes, prediabetes, and gestational diabetes. Because it is cumbersome, this test is not routinely used except for diagnosing gestational diabetes.

100-Gram Oral Glucose Tolerance Test
for Gestational Diabetes (mg/dL)*


95 or higher

1 hour after

180 or higher

2 hours after

155 or higher

3 hours after

140 or higher


*Gestational diabetes is diagnosed when measurements at 2 or more of the time points are too high.


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