For adults and pregnant women asked to have an oral glucose tolerance test.
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Before the test
- For 3 days before: eat your normal meals. Do not diet or cut down rice and roti. Dieting can give a false result.
- The night before: eat dinner, then nothing for at least 8 hours, and not more than 14. Plain water is allowed.
- On the morning: no tea, coffee, breakfast, smoking or tobacco. Do not exercise. Ask your doctor about your morning tablets and bring them with you.
At the laboratory
- A fasting blood sample is taken.
- You drink 75 grams of glucose dissolved in a glass of water (250 to 300 ml). Finish it within 5 minutes.
- The 2 hours are counted from the moment you start drinking.
- Sit quietly for the 2 hours. No food, tea, coffee, smoking or walking about. A few sips of plain water are fine.
- A second blood sample is taken at 2 hours. Some pregnant women also have a sample at 1 hour.
- Eat after the last sample. Bring a snack.
Keep the whole morning free: the test takes about two and a half hours. The drink is very sweet and can cause nausea or light-headedness. Tell the staff if you feel unwell. If you vomit, tell them: the test may need to be repeated on another day.
If you are pregnant
Many doctors in India use a simpler test: 75 grams of glucose taken at any time, whether or not you have eaten, with one blood sample 2 hours later. A result of 140 mg/dL or more means gestational diabetes, the diabetes that appears in pregnancy. Others use the fasting test with three samples. Your doctor marks above whether you must fast.
What the results mean (adults who are not pregnant)
| Normal | Prediabetes | Diabetes | |
|---|---|---|---|
| Fasting | below 100 | 100 to 125 | 126 or more |
| 2 hours after glucose | below 140 | 140 to 199 | 200 or more |
Values in mg/dL, using the American Diabetes Association cut-offs. Your doctor will read the result along with your symptoms and other tests.
Postpone the test and tell us if
- You have fever or any illness, or were in hospital recently
- You are taking steroid tablets or injections
- You already have diabetes diagnosed: this test is not needed
Questions about this sheet? Call Caspian Healthcare reception on +91 89193 41154. A doctor is on duty at all hours for problems that are not critical. Caspian has no emergency department: in an emergency call 108.
Where this comes from
- World Health Organization 1999: definition, diagnosis and classification of diabetes, Annex 1, the oral glucose tolerance test (copy hosted by Newcastle University)
- American Diabetes Association Standards of Care 2025: diagnosis and classification of diabetes
- Ministry of Health and Family Welfare: diagnosis and management of gestational diabetes, technical and operational guidelines, 2018
Prepared by Caspian Healthcare from the sources above. Last reviewed October 2026. General information: your own doctor's written instructions come first.