Tests and diagnosisBy Mayo Clinic staff
Who should be tested
The American Diabetes Association recommends blood glucose screening if you have any risk factors for prediabetes. This includes if you:
- Are overweight, with a body mass index above 25
- Are inactive
- Are age 45 or older
- Have a family history of type 2 diabetes
- Are African-American, Hispanic, American Indian, Asian-American or a Pacific Islander
- Have a history of gestational diabetes or have given birth to a baby who weighed more than 9 pounds (4.1 kilograms)
- Have a history of polycystic ovary syndrome
- Have high blood pressure
- Have abnormal cholesterol levels, including a high-density lipoprotein (HDL) cholesterol below 35 mg/dL (0.9 mmol/L) or triglyceride level above 250 mg/dL (2.83 mmol/L)
Tests used to diagnose prediabetes
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.
Certain conditions can make the A1C test inaccurate — such as if you are pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant).
Following are other tests that your doctor may use to diagnose prediabetes:
- 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) — 5.6 millimoles per liter (mmol/L) — is normal. A blood sugar level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes. This is sometimes referred to as impaired fasting glucose (IFG). A blood sugar level of 126 mg/dL (7.0 mmol/L) or higher may indicate diabetes mellitus.
- 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 (7.8 mmol/L) is normal. A blood sugar level from 140 to 199 mg/dL (7.8 to 11.0 mmol/L) is considered prediabetes. This is sometimes referred to as impaired glucose tolerance (IGT). A blood sugar level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes mellitus.
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. For example, your doctor should check your fasting blood sugar, A1C, total cholesterol, HDL cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides at least once a year, possibly more frequently if you have additional risk factors for diabetes. Your doctor may also recommend an annual microalbuminuria test, which checks for protein in your urine — an early sign of damage to the kidneys.
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