Tests and Diagnosis

An international committee composed of experts from the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation recommends that type 2 diabetes testing include the:

  • Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It works by measuring the percentage of blood sugar attached to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your blood sugar levels, the more hemoglobin you’ll have with sugar attached. An A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 5.7 and 6.4 percent is considered prediabetes, which indicates a high risk of developing diabetes.

If the A1C test isn’t available, or if you have certain conditions that can make the A1C test inaccurate — such as if you’re pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — your doctor may use the following tests to diagnose diabetes:

  • Random blood sugar test. A blood sample will be taken at a random time. Regardless of when you last ate, a random blood sugar level of 200 milligrams per deciliter (mg/dL) or higher suggests diabetes.
  • Fasting blood sugar test. A blood sample will be taken after an overnight fast. A fasting blood sugar level less than 100 mg/dL is normal. A fasting blood sugar level from 100 to 125 mg/dL is considered prediabetes. If it’s 126 mg/dL or higher on two separate tests, you’ll be diagnosed with diabetes.

An oral glucose tolerance test may also be performed. For this test, you fast overnight, and the fasting blood sugar level is measured. Then, you drink a sugary liquid, and blood sugar levels are tested periodically for the next several hours. A reading of more than 200 mg/dL after two hours indicates diabetes. A reading between 140 and 199 mg/dL indicates prediabetes.

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 135/80 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 — which often require different treatment strategies because in type 1 diabetes, the pancreas no longer makes insulin.

After the diagnosis
A1C levels need to be checked between two and four times a year. Your target A1C goal may vary depending on your age and various other factors. However, for most people, the American Diabetes Association recommends an A1C level below 7 percent. Ask your doctor what your A1C target is.

The American Diabetes Association has recently introduced a formula that translates the A1C into what’s known as an estimated average glucose (eAG). The eAG more closely correlates with daily blood sugar readings. An A1C of 7 percent translates to an eAG of 154 mg/dL. That would mean that your average blood sugar levels are around 150 mg/dL.

Compared with repeated daily blood sugar tests, A1C testing better indicates how well your diabetes treatment plan is working. An elevated A1C level may signal the need for a change in your medication or meal plan.

In addition to the A1C test, the doctor will also take blood and urine samples periodically to check your cholesterol levels, thyroid function, liver function and kidney function. The doctor will assess your blood pressure. Regular eye and foot exams also are important.