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Diabetes tests and diagnosis: what your results mean
Key takeaways
- Diabetes is diagnosed with A1C ≥ 6.5%, fasting glucose ≥ 126 mg/dL, 2-hour OGTT ≥ 200 mg/dL, or a random glucose ≥ 200 mg/dL with symptoms.
- Without clear symptoms, a high result is usually confirmed with a repeat test.
- The ADA recommends screening all adults from age 35, and earlier with overweight plus risk factors.
- Home meters and CGMs are for monitoring — they don't replace lab diagnosis.
Diagnostic cutoffs
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| A1C | Below 5.7% | 5.7–6.4% | 6.5% or higher |
| Fasting plasma glucose (8+ hours) | Below 100 mg/dL | 100–125 mg/dL | 126 mg/dL or higher |
| 2-hour oral glucose tolerance test (75 g) | Below 140 mg/dL | 140–199 mg/dL | 200 mg/dL or higher |
| Random glucose | — | — | 200 mg/dL or higher with classic symptoms |
Cutoffs from the American Diabetes Association and CDC.
The tests explained
A1C (hemoglobin A1c)
Shows your average blood sugar over about 2–3 months. No fasting needed. Some conditions — such as anemia, certain hemoglobin variants, pregnancy, or recent blood loss — can make it less accurate. See the A1C chart to convert A1C to average glucose.
Fasting plasma glucose
A blood draw after at least 8 hours without food or caloric drinks, usually in the morning.
Oral glucose tolerance test (OGTT)
You fast, drink a sweet glucose solution, and have blood drawn after 2 hours. It's more sensitive and is also used in pregnancy.
Random glucose
A blood test at any time of day. A level of 200 mg/dL or higher together with symptoms like thirst, frequent urination, and weight loss can confirm diabetes.
Who should get tested?
- All adults age 35 and older (ADA), repeated at least every 3 years if normal
- Younger adults with overweight plus a risk factor such as family history, high blood pressure, PCOS, or physical inactivity
- Anyone with prediabetes — usually yearly
- People who had gestational diabetes — at least every 3 years
- Anyone with symptoms of diabetes
After a diagnosis
Your doctor may order antibody tests (to check for type 1 or LADA), kidney and cholesterol tests, and an eye exam. Then you'll agree on targets and a management plan.
Cardivo keeps lab results and home readings together in one timeline you can export as a PDF.
This guide is general wellness education based on the public sources below. It is not medical advice, diagnosis, or treatment. Cardivo is not a medical device. If you think you are having a medical emergency, call 911.
Frequently asked questions
What A1C level means diabetes?
An A1C of 6.5% or higher is in the diabetes range; 5.7–6.4% is prediabetes. A high result is usually confirmed with a repeat test unless symptoms are clear.
Do I need to fast for a diabetes test?
You need to fast at least 8 hours for a fasting glucose test or an OGTT. The A1C test does not require fasting.
At what age should you get tested for diabetes?
The American Diabetes Association recommends screening all adults starting at age 35, and earlier for people with overweight and additional risk factors.