Type 2 diabetes is usually diagnosed using the:
- Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. Normal levels are below 5.7 percent, and a result between 5.7 and 6.4 percent is considered prediabetes. An A1C level of 6.5 percent or higher on two separate tests means you have diabetes.
If the A1C test isn’t available, or if you have certain conditions — such as an uncommon form of hemoglobin (known as a hemoglobin variant) — that interfere with A1C test, your doctor may use the following tests to diagnose diabetes:
- Random blood sugar test. Blood sugar values are expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). Regardless of when you last ate, a blood sample showing that your blood sugar level is 200 mg/dL (11.1 mmol/L) or higher suggests diabetes, especially if you also have signs and symptoms of diabetes, such as frequent urination and extreme thirst.
- Fasting blood sugar test. A blood sample is taken after an overnight fast. A reading of less than 100 mg/dL (5.6 mmol/L) is normal. A level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes.If your fasting blood sugar is 126 mg/dL (7 mmol/L) or higher on two separate tests, you have diabetes.
- Oral glucose tolerance test. This test is less commonly used than the others, except during pregnancy. You’ll need to fast overnight and then drink a sugary liquid at the doctor’s office. Blood sugar levels are tested periodically for the next two hours.A blood sugar level less than 140 mg/dL (7.8 mmol/L) is normal. A reading between 140 and 199 mg/dL (7.8 mmol/L and 11.0 mmol/L) indicates prediabetes. A reading of 200 mg/dL (11.1 mmol/L) or higher after two hours suggests diabetes.
The American Diabetes Association recommends routine screening for type 2 diabetes beginning at age 45, especially if you’re overweight. If the results are normal, repeat the test every three years.
If the results are borderline, ask your doctor when to come back for another test.Screening is also recommended for people who are under 45 and overweight if there are other heart disease or diabetes risk factors present, such as a sedentary lifestyle,
a family history of type 2 diabetes, a personal history of gestational diabetes or blood pressure above 140/90 millimeters of mercury (mm Hg).If you’re diagnosed with diabetes, the doctor may do other tests to distinguish between type 1 and type 2 diabetes — since the two conditions often require different treatments.
