A diagnosis of diabetes

The test results that confirm a diabetes diagnosis are:

• An A1C level of 6.5% or higher.

• A fasting plasma glucose (FPG) level of 126 mg/dL or higher. Fasting means not eating or drinking except water for at least 8 hours.

• A random plasma glucose level of 200 mg/dL or higher, with the symptoms of high blood sugar (hyperglycemia) or hyperglycemic crisis. This level can be measured at any time of day.

• An oral glucose tolerance test level of 200 mg/dL or higher. For this test, you fast for at least 8 hours. Then you drink a sweet liquid that has a certain amount of glucose.

If you don't have symptoms of hyperglycemia, a diagnosis needs 2 abnormal test results from the same sample, or from 2 separate test samples. For example, an FPG of more than 126 and an A1C of more than 6.5% would be needed to diagnose diabetes.

Some conditions can affect the accuracy of the A1C test. These include:

• Sickle cell disease.

• Severe anemia.

• Liver disease.

• Pregnancy (early or late pregnancy).

• Glucose-6-phosphate dehydrogenase deficiency.

• HIV (and some HIV medicines).

• Kidney failure (hemodialysis).

• Recent blood loss or blood transfusion.

• Erythropoietin therapy.

A diagnosis of gestational diabetes

Gestational diabetes is diabetes that starts during pregnancy with no previous history of diabetes. Anyone who is at risk for type 2 diabetes should be tested for diabetes at their first prenatal visit. This is done using the standard tests above. More tests to check for gestational diabetes will be done later in pregnancy. Gestational diabetes may be diagnosed with one of the methods below.

One-step method

This is a 75-gram glucose tolerance test. For this test, you drink a sweet glucose drink. Blood sugar levels are checked after you have fasted for at least 8 hours. They are also checked 1 hour after the drink and 2 hours after the drink. This test is done at 24 to 28 weeks' gestation when you have not been diagnosed with diabetes before. Gestational diabetes is diagnosed when you have one of these blood sugar levels: 

• Fasting: 92 mg/dL or higher

• 1 hour: 180 mg/dL or higher

• 2 hour: 153 mg/dL or higher

Two-step method

This test is also done at 24 to 28 weeks' gestation if you have not been diagnosed with diabetes.

Step 1. A 50-gram glucose tolerance test with a blood sugar level check at 1 hour. If the blood sugar at 1 hour is 130 to 140 mg/dL or higher, then go to step 2.  

Step 2. A100-gram glucose tolerance test is done while you are fasting. Gestational diabetes is diagnosed when you have at least two of these blood sugar levels:

• Fasting: 95 mg/dL or higher

• 1 hour: 180 mg/dL or higher

• 2 hour: 155 mg/dL or higher

• 3 hour: 140 mg/dL or higher

Talk with your doctor about being screened for gestational diabetes. If you are diagnosed with gestational diabetes, you should be tested for prediabetes or diabetes at 4 to 12 weeks postpartum.