Prediabetes and early type 2 diabetes usually cause no symptoms. A simple blood test can find them years before complications start.
More than one in three American adults has prediabetes, according to the CDC, and most don’t know it. Screening finds it while there’s still plenty of time to change course.
Who should be screened
- The U.S. Preventive Services Task Force recommends screening adults aged 35 to 70 who have overweight or obesity.
- The American Diabetes Association recommends testing all adults from age 35, and earlier for people with risk factors.
Risk factors include a parent or sibling with diabetes, a history of gestational diabetes, polycystic ovary syndrome, physical inactivity, high blood pressure, and belonging to groups with higher rates of diabetes, such as Black, Hispanic or Latino, American Indian, Alaska Native, Asian American and Pacific Islander adults.
The tests and what results mean
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| A1C (average blood sugar over about three months) | Below 5.7% | 5.7% to 6.4% | 6.5% or higher |
| Fasting plasma glucose | Below 100 mg/dL | 100 to 125 mg/dL | 126 mg/dL or higher |
| Two-hour oral glucose tolerance test | Below 140 mg/dL | 140 to 199 mg/dL | 200 mg/dL or higher |
A diabetes diagnosis normally needs two abnormal results, either from the same sample or on separate days, unless symptoms make it obvious. Some conditions, such as certain anemias, can make A1C less reliable, so your clinician may choose a different test.
Please note
The A1C test doesn’t require fasting, which makes it convenient. Fasting glucose requires no food or drink other than water for at least eight hours.
If you have prediabetes
This is the moment screening is designed for. The CDC-recognized National Diabetes Prevention Program, a year-long lifestyle change program, has been shown to cut the risk of developing type 2 diabetes by more than half in people with prediabetes. Many programs are online, and some insurers and Medicare cover them.
If you have diabetes
A diagnosis comes with a plan: regular A1C checks, eye and foot exams, kidney tests, blood pressure and cholesterol management, and support with food and activity. Early treatment lowers the risk of complications.
Diabetes and cholesterol both feed into your heart risk. For how screening fits into a regular visit, see our guide to the preventive checkup.
Key points
- The Task Force recommends screening adults 35 to 70 who have overweight or obesity; the American Diabetes Association recommends testing all adults starting at 35.
- An A1C of 5.7% to 6.4% indicates prediabetes, and 6.5% or higher, confirmed by repeat testing, indicates diabetes.
- A fasting glucose of 100 to 125 mg/dL indicates prediabetes, and 126 or higher indicates diabetes.
- Prediabetes is common and often reversible; structured lifestyle programs can sharply lower the chance of developing type 2 diabetes.
Common questions
Should I be tested before 35?
Yes, if you have risk factors such as a family history of diabetes, a history of gestational diabetes or polycystic ovary syndrome, or belong to a group with higher rates of diabetes. Ask your clinician.
Can a home glucose monitor diagnose diabetes?
No. A diagnosis is based on laboratory tests such as A1C or fasting plasma glucose, usually confirmed with a repeat test.
How often should I be retested?
If your results are normal, repeating the test about every three years is common advice. People with prediabetes are usually retested more often.
This guide explains general U.S. screening recommendations and is not medical advice. Your clinician may recommend a different schedule based on your health, history and test results.