What diabetes screening tests measure

Diabetes screening looks for high blood sugar levels before you have symptoms. Three tests can detect it: a fasting blood glucose test (blood drawn after not eating for eight hours), a hemoglobin A1C test (shows your average blood sugar over three months), or an oral glucose tolerance test (blood drawn two hours after drinking a sugary liquid). Any of these can catch diabetes or prediabetes, a stage where blood sugar is higher than normal but not yet diabetic.

The A1C test is the most common because you do not have to fast, and it reflects your actual blood sugar control over time rather than one moment. Your doctor will order whichever test makes sense for your situation and may repeat it to confirm a result.

Key Takeaways

  • The American Diabetes Association recommends screening starting at age 45, or earlier if you are overweight or have other risk factors like high blood pressure or a family history of diabetes.
  • A fasting glucose test, A1C test, or glucose tolerance test can all detect diabetes, and your doctor chooses based on your health history.
  • Screening is usually covered by insurance with no out-of-pocket cost, and many community health centers offer it for free or low cost if you are uninsured.
  • If screening shows prediabetes, lifestyle changes like weight loss and exercise can often prevent or delay type 2 diabetes from developing.

Who should be screened and when

The American Diabetes Association recommends screening for all adults starting at age 45. If you are younger than 45, you should still be screened if you are overweight (BMI of 25 or higher), have high blood pressure, have a parent or sibling with diabetes, are not physically active most days, or belong to certain ethnic groups at higher risk—including Black, Hispanic, Native American, Asian American, and Pacific Islander populations.

If your first screening is normal, you should be retested every three years. If you have prediabetes, your doctor may recommend screening every year or more often. Pregnant women are screened for gestational diabetes between weeks 24 and 28 of pregnancy, which is a separate test from regular diabetes screening.

Where to get screened

Your primary care doctor can order a diabetes screening at a routine visit. You can also get screened at urgent care clinics, community health centers, or at some pharmacies that offer health screenings. Many employers offer screening as part of workplace wellness programs, and some health fairs in your community include free or low-cost screening.

If you do not have a doctor, call 211 (a free referral line) to find a community health center near you that offers screening on a sliding fee scale based on income. Federally may have access to Health Centers (FQHCs) are required to screen for chronic diseases and often have same-day or next-day appointments.

What to expect during screening

For a fasting glucose test, you will need to avoid food and drink (except water) for eight hours before your appointment, usually overnight. The test itself takes a few minutes—a nurse draws blood from your arm, and you can eat normally afterward. Results are usually available within a few days.

An A1C test requires no fasting. A small blood sample is drawn and sent to a lab; results typically come back within a week. A glucose tolerance test takes longer—you fast overnight, have blood drawn, drink a sweet liquid, wait two hours, and have blood drawn again. This test is less common unless your doctor suspects gestational diabetes or wants a more detailed picture.

Understanding your results

A fasting glucose under 100 mg/dL is normal. Between 100 and 125 mg/dL is prediabetes. At 126 mg/dL or higher, a second test confirms type 2 diabetes. For A1C, below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or higher indicates diabetes. Your doctor will explain what your specific numbers mean and what to do next.

If you have prediabetes, the good news is that lifestyle changes work. Studies show that losing 5% to 10% of your body weight and exercising 150 minutes per week can reduce your risk of developing diabetes by about 58%. Your doctor may refer you to a diabetes prevention program, which teaches nutrition and exercise strategies in a group setting.

Cost and insurance coverage

Most insurance plans cover diabetes screening with no out-of-pocket cost if your doctor orders it as a preventive service. Medicare covers screening for all beneficiaries at no cost. If you are uninsured, community health centers and FQHCs charge on a sliding scale based on what you earn, and some offer screening for free.

Pharmacy-based screenings (at chains like CVS or Walgreens) may cost $25 to $50 out of pocket, though some are free during health awareness events. Ask the pharmacy or clinic what the cost will be before you have blood drawn.

What happens after screening

If your screening is normal, your doctor will tell you when to return for your next one—usually in three years. If you have prediabetes, your doctor will discuss lifestyle changes and may refer you to a diabetes prevention program. The CDC's National Diabetes Prevention Program is available in most states and teaches weight loss, nutrition, and exercise in weekly classes; some programs are offered online or by phone.

If you are diagnosed with diabetes, your doctor will order additional tests (kidney function, cholesterol, eye exam) and discuss treatment options. You will likely be referred to a diabetes educator or nutritionist. Early diagnosis means you can start managing blood sugar before complications develop, which is why screening matters even when you feel fine.

Frequently Asked Questions

Do I need to fast before a diabetes screening?

Only for a fasting glucose test. An A1C test, which is more common, requires no fasting. Ask your doctor which test they are ordering so you know whether to skip breakfast.

Can diabetes screening be done at home?

Home glucose meters measure blood sugar if you already have diabetes, but they are not used for initial screening. Screening requires a lab test ordered by a doctor or health provider to may support accuracy.

What if my screening shows prediabetes—does that mean I will get diabetes?

No. Prediabetes means your blood sugar is higher than normal, but lifestyle changes can stop it from progressing. Studies show that weight loss and regular exercise prevent or delay diabetes in most people with prediabetes.

How often should I be screened if I have risk factors?

If you have prediabetes or risk factors like high blood pressure or obesity, your doctor may recommend screening every year instead of every three years. Ask your doctor what schedule makes sense for you.

Is screening covered if I have no symptoms?

Yes. Preventive screening is covered by most insurance plans at no cost, even if you have no symptoms. Medicare covers it for all beneficiaries. If you are uninsured, community health centers offer screening on a sliding fee scale.