I. Principle
Oral glucose tolerance test is also called OGTT (oral glucose tolerance test). After a normal person ingests a large amount of glucose at one time, the blood glucose concentration will rise slightly, but generally will not exceed 8.88mmol/L, and the blood glucose will return to normal within 2 hours. If the patient has glucose metabolism disorder, after consuming a large amount of glucose, the blood sugar will rise sharply and will not return to normal within 2 hours.
II. Method
① Glucose dose
The dose of glucose for OGTT experiment was confusing in the past, useful for 100g, 75g, and 50g. For example, in the past, screening for gestational diabetes used the so-called two-step method, first taking 50g of glucose, and then measuring the glucose 1h after taking glucose ≥ 7.8 mmol/L for a positive screening, and then conducting the oral glucose tolerance test with 75g of glucose. Now the standards are unified and all perform the glucose tolerance test with 75g of oral glucose. Adults are given 75g of anhydrous glucose (available at our hospital pharmacy in a packet of 75g), dissolved in 200-300ml of water, to be consumed within 5 minutes, and nothing else to be eaten between the oral administration of 75g of glucose and the end of the test.
② Time point of the test
If you are non-pregnant and just doing the test to rule out diabetes, then you only need to test the blood glucose 2h after fasting and sugar (note that this time is counted from the first sip of sugar water).
In case of pregnant women, according to the latest revised standard of American Diabetes Association 2011, only fasting, 1h postprandial and 2h postprandial blood glucose need to be tested.
③ Result interpretation: 2h blood glucose ≥ 11.1mmol/L after taking sugar for non-pregnant women, and if the patient has typical symptoms of diabetes (excessive drinking, excessive urination and unexplained wasting) then diabetes can be diagnosed. If there is no symptom, it should be confirmed by retesting at a later date.
Fasting blood sugar ≥5.1mmol/L for pregnant women
1h blood glucose≥10mmol/L after taking sugar
2h blood sugar≥8.5mmol/L
GDM can be diagnosed as long as the blood glucose at any of the above three time points exceeds the standard.
Applicable people
Any patient with impaired glucose regulation should have an OGTT test. This includes the following conditions
① IFG (impaired fasting glucose): If the patient has 6.1 mmol/L ≤ fasting glucose <7.0 mmol/L, OGTT should be performed.
② IGT (impaired glucose tolerance): if the patient has 7.8 mmol/L ≤ 2h postprandial glucose <11.1 mmol/L, OGTT should be performed.
③ In the past, we used to use fasting blood glucose to screen for diabetes in clinical practice, and the vast majority of patients who underwent physical examination drew fasting blood glucose. However, epidemiological surveys show that a significant number of diabetic patients have normal fasting glucose and only show high postprandial 2h glucose, so if we only check fasting glucose, we may have to miss 75% of diabetic patients. Therefore, I think that if outpatients want to rule out diabetes, they should do OGTT.
Four, OGTT precautions
① OGTT should be performed in a fasting state, and the fasting time should not be less than 10 hours or more than 16 hours (eat at 6 pm and check before 10 am the next day).
② Sufficient calories of carbohydrates should be consumed 3 days before the test, otherwise it is easy to lower the glucose tolerance and have a false positive.
③ Strenuous physical activity should not be performed before or after the OGTT test.
④ Avoid mental stimulation during the OGTT test.
⑤ Stop taking oral contraceptives 1 week before the OGTT test
Stop taking niacin or diuretics 3-4 days before the test
Stop 3 days before oral salicylic acid or insulin
Stop 1 month before taking oral monoamine oxidase inhibitors
(6) OGTT is not recommended for all kinds of physiological stress (excessive excitement, excessive physical activity) and all kinds of pathological stress (fever, infection, trauma, surgery, anesthesia, coma).