What is this test?
Also known as the glucose challenge test. After a first blood sample is taken on an empty stomach, a sugary drink containing 75 grams of glucose is consumed and blood is drawn again at set intervals. By showing how the body handles sugar, it helps diagnose diabetes and prediabetes; you will need to wait at the laboratory for the duration of the test.
When is it requested?
The sample should be collected after an average of 10-16 hours of fasting, and the test should start between 08:00 and 10:00. During the test, the patient must not eat, drink or smoke and should avoid strenuous exertion. 75 g of glucose is given orally. Glucose is measured in blood samples collected once immediately before the glucose load and at 60 and 120 minutes afterward.
What does a high glucose tolerance test (OGTT) result mean?
High readings after the glucose drink mean your body can't clear sugar quickly enough; this may suggest prediabetes, diabetes or gestational diabetes.
- Cutting carbohydrates sharply in the days before the test (falsely high result)
- Smoking, walking around or stress during the test
- Acute illness, or medicines such as corticosteroids or some diuretics
- Impaired glucose tolerance (prediabetes)
- Gestational diabetes
- Diabetes
What does a low glucose tolerance test (OGTT) result mean?
A drop in blood sugar at the later readings may be due to excess insulin release after the glucose drink (reactive hypoglycemia); it is usually not serious.
- Exaggerated insulin response to the glucose drink (reactive hypoglycemia)
- Early insulin resistance
- After stomach or weight-loss surgery (dumping syndrome)
- Delayed processing of the blood samples
My result is outside the reference range. What should I do?
Eat normally for 3 days before the test and arrive after an 8–12 hour fast; during the test, stay seated, don't eat and don't smoke. Your doctor interprets the results, using separate criteria in pregnancy.
Reference ranges depend on the method, age and sex; always use the range printed on your report. This information is for general guidance only; consult your doctor for diagnosis and treatment.
Sample information
- Sample type: Serum
- Tube / container: Red / yellow-top tube
- Sample volume: 1 mL
Preparation
No special preparation is required. If you are unsure, ask us before your blood draw.
Testing and results
- Method: PHOT
- Run schedule: Daily at 09:00
- Turnaround time: Same day, 18:00
Price and appointment
Add the test to your list to receive a price quote by e-mail, or call +90 850 640 07 30 / message us on WhatsApp (+90 537 301 22 14). You can have the test done at our branches or with our home blood collection service. Results can be viewed online with your Turkish ID number (or passport number for foreign nationals).