Oral Glucose Tolerance Test
The last test given is called an oral glucose tolerance test. The patient needs to fast, usually overnight, for 10-16 hours before the test is taken. The only thing that can be ingested is water. Once at the doctor's office, a blood sample is drawn and tested to give a baseline reading. While waiting for the results of the first test, the patient is given a drink of glucola, a cola drink that has a high content of sugar (75 grams of glucose). If the person being tested is a pregnant woman, a higher dose of glucola (100 grams) is given.
Another blood test is taken 30 minutes after the glucola has been ingested and is able to be absorbed into the bloodstream. Blood tests will continue to be drawn after 1, 2 and 3 hours after drinking the glucola. Each of the 5 tests are analyzed to see how the body has responded to the glucola.
The person taking the test must be in good health to be able to rely on the results of the test. Unfortunately, something as simple as a cold or other illness can skew the results enough to give a false readings. Also, it is imperative that the test be taken after fasting. Even drinking black coffee or having a cigarette make change the levels.
While the oral glucose tolerance test is being taken, the patient should not be active. It's best to have a book to read or watch television in between tests to pass the time.
Having 5 blood tests over the period of 3 hours after drinking glucola will show the rise and fall of blood sugar levels over time. A person who does not have diabetes will have a spike in blood glucose levels and then they will quickly return to normal. However, a person with diabetes will not be able to tolerate the glucola and their levels will spike and then gradually decrease at a much slower rate. Even if the test shows high levels of blood glucose, the oral glucose tolerance test will be taken a second time before a formal diagnosis of diabetes is made to ensure there are no outside factors that might have skewed the results.