Various factors may have an impact on glucose tolerance test values, including food consumption, exercise, and certain medications. Patients should follow all doctor instructions before and during testing to ensure accurate results. Most times, patients are only allowed to consume water during the period of testing and for several hours beforehand as well.
A glucose tolerance test can last anywhere from one to four or more hours, depending on initial results. Patients who are being tested for either gestational or type 2 diabetes are asked to refrain from eating for several hours prior to testing. Upon arrival at the doctor's office or clinic, patients drink a water solution containing glucose. They are then tested one hour later to check for high blood sugar. If this test shows spiked blood glucose levels or is inconclusive, additional tests may be conducted in which blood sugar is tested one, two, and three or more hours after glucose consumption.
Many factors may affect glucose tolerance test values. The first, and one of the most common, is consuming food or drink during the testing period. This can artificially raise blood sugar higher than normal and may lead to a false diagnosis of diabetes. For this reason, patients should make sure they are very clear on when to stop eating and drinking anything other than plain water and for how long this process should continue.
Exercise directly before or during testing may also impact glucose tolerance test values. This is because working out alerts the body that more glucose is needed in order to function, resulting in faster glucose consumption and lower overall blood sugar. Those who are diabetic may experience increased blood sugar when exercising vigorously because the body releases glucose faster than it can be used. Both of these things may skew test results in one direction or the other.
There are also certain medications which may affect glucose tolerance test values. Any pills or drugs containing any form of sugar may raise blood glucose levels. Medications which affect insulin production or the metabolism may also impact blood sugar by causing the body to burn sugar faster or slower than usual. Patients who are unsure of whether a medication they are taking may impact test results should discuss it with a doctor prior to testing. In some cases, the drug may be temporarily discontinued or lowered to allow for more accurate results.