Getting a type 2 diabetes diagnosis starts with a simple blood test, usually ordered by your primary care doctor. Three main tests can confirm the diagnosis, each with specific cutoff numbers. Most require only a blood draw, and at least one doesn’t even need fasting. If you’re experiencing symptoms or have risk factors, getting tested is straightforward.
Who Should Get Tested
Many people with type 2 diabetes live with it for years before finding out, because symptoms develop gradually. You might not notice anything unusual, or you might chalk up fatigue and extra thirst to stress or aging. Common signs that prompt testing include increased thirst and urination, unexplained weight loss, blurred vision, slow-healing sores, frequent infections, and numbness or tingling in your hands or feet. Some people notice darkened patches of skin, particularly around the neck and armpits.
Even without symptoms, current guidelines recommend screening starting at age 35, repeated every three years. If you’re under 35 but carry extra weight and have at least one additional risk factor (family history, high blood pressure, abnormal cholesterol, or a history of gestational diabetes), you should be screened earlier. The same diagnostic thresholds apply to children and adolescents, though pediatric screening typically targets kids with obesity and additional risk factors.
The Three Diagnostic Blood Tests
Your doctor will use one of three standard blood tests. Each measures blood sugar differently, and any one of them can lead to a diagnosis.
A1C Test
The A1C test (also called hemoglobin A1C) measures your average blood sugar over the past two to three months. It doesn’t require fasting, so you can have it done at any time of day regardless of when you last ate. An A1C below 5.7% is considered healthy. A result between 5.7% and 6.4% indicates prediabetes. A result of 6.5% or higher on two separate tests means diabetes.
This is often the first test doctors order because it’s convenient and gives a longer-term picture rather than a single-moment snapshot. Certain conditions, like sickle cell disease or recent blood transfusions, can affect accuracy, in which case your doctor will use one of the other tests instead.
Fasting Plasma Glucose Test
This test measures your blood sugar after you haven’t eaten for 8 to 12 hours (water is fine). You’ll typically schedule a morning appointment and skip breakfast. A fasting level below 100 mg/dL is normal. Between 100 and 125 mg/dL falls in the prediabetes range. A fasting result of 126 mg/dL or higher indicates diabetes.
Oral Glucose Tolerance Test
The oral glucose tolerance test (OGTT) is more involved. You fast overnight, have your blood drawn, then drink a sugary solution provided by the lab. Two hours later, your blood is drawn again. A two-hour reading of 200 mg/dL or higher confirms diabetes. Results between 140 and 199 mg/dL indicate prediabetes. This test is less commonly used for routine screening because it takes longer and requires you to stay at the lab, but it’s particularly useful when other test results are borderline.
What Happens at the Appointment
If you’re going in specifically to check for diabetes, the visit is usually quick. Tell your doctor about any symptoms you’ve noticed and any family history of diabetes. For a fasting test, you’ll need to avoid food and drinks other than water for 8 to 12 hours beforehand. Your provider will tell you the exact timeframe. For an A1C test, no preparation is needed.
The blood draw itself takes a few minutes. Results from a lab typically come back within a day or two, though some offices have point-of-care A1C machines that return results during your visit.
Why You Usually Need Two Tests
A single abnormal result generally isn’t enough for a formal diagnosis. Guidelines call for a confirmatory test, either a repeat of the same test or a different one, performed on a separate day. For example, if your first A1C comes back at 6.7%, your doctor will order a second A1C or a fasting glucose test to confirm. The one exception: if you have classic diabetes symptoms (extreme thirst, frequent urination, unexplained weight loss) and a random blood sugar of 200 mg/dL or higher, that single result plus symptoms is enough for diagnosis without a second test.
This two-test requirement exists because blood sugar levels can fluctuate from stress, illness, or medication. Confirming on a separate day reduces the chance of a false diagnosis.
Prediabetes Results
If your numbers land in the prediabetes range (A1C of 5.7% to 6.4%, fasting glucose of 100 to 125 mg/dL, or a two-hour OGTT of 140 to 199 mg/dL), you don’t have diabetes yet, but your blood sugar is higher than normal. This is actually valuable information because prediabetes is often reversible with lifestyle changes like weight loss and increased physical activity. Your doctor will likely recommend retesting in one to three years, or sooner if your risk factors are significant.
Cost and Insurance Coverage
Diabetes screening is classified as a preventive service, which means most insurance plans cover it at no out-of-pocket cost when your doctor determines you’re at risk. Medicare Part B covers up to two blood glucose screening tests per year for eligible adults, including fasting glucose and A1C tests, with no copay when your provider accepts Medicare assignment. Eligibility includes having high blood pressure, abnormal cholesterol, obesity, or a history of high blood sugar. You also qualify if two or more of the following apply: you’re 65 or older, overweight, have a family history of diabetes, or have a history of gestational diabetes.
If you’re uninsured, community health centers and free clinics often offer diabetes screening. An A1C test without insurance typically costs between $20 and $50 at a lab.
After a Diagnosis
Once type 2 diabetes is confirmed, your doctor will discuss a management plan tailored to your situation. This usually starts with lifestyle modifications (dietary changes, exercise, weight management) and may include medication depending on how high your blood sugar levels are at diagnosis. You’ll also get baseline tests to check for any early complications, including kidney function, cholesterol levels, and an eye exam.
Your A1C will become a regular part of your life going forward. Most people with diabetes have it checked every three to six months to track how well their blood sugar is being managed over time. The same test that diagnosed you becomes the primary tool for monitoring your progress.