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Tests and diagnosis
By Mayo Clinic staffThe American College of Endocrinology suggests prediabetes testing for anyone who has a family history of type 2 diabetes and for those who are obese or have metabolic syndrome. Women with a personal history of gestational diabetes also should be tested.
In June 2009, an international committee composed of experts from the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation recommended that prediabetes 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 between 6 and 6.5 percent is considered prediabetes. A level of 6.5 percent or higher on two separate tests indicates you have 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:
- Fasting blood sugar test. A blood sample will be taken after you fast for at least eight hours or overnight. With this test, a blood sugar level lower than 100 milligrams per deciliter (mg/dL) is normal. A blood sugar level from 100 to 125 mg/dL is considered prediabetes. This is sometimes referred to as impaired fasting glucose (IFG). A blood sugar level of 126 mg/dL or higher may indicate diabetes.
- Oral glucose tolerance test. A blood sample will be taken after you fast for at least eight hours or overnight. Then you'll drink a sugary solution, and your blood sugar level will be measured again after two hours. A blood sugar level less than 140 mg/dL is normal. A blood sugar level from 140 to 199 mg/dL is considered prediabetes. This is sometimes referred to as impaired glucose tolerance (IGT). A blood sugar level of 200 mg/dL or higher may indicate diabetes.
If your blood sugar level is normal, your doctor may recommend a screening test every three years. If you have prediabetes, further testing may be needed. Your doctor may recommend a glucose tolerance test once a year. This test can identify individuals who have diabetes sooner than the fasting blood glucose test can. Your doctor may also recommend an annual microalbuminuria test, which checks for protein in your urine — an early sign of damage to the kidneys. Twice a year, your doctor should check your fasting blood sugar and A1C levels. Your blood fats — total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides — also need to be checked twice a year.
