An overview of Glucose Tolerance Test
A glucose tolerance test is a medical test that measures how your body responds to sugar (glucose) after consuming a sweet drink. It is often used to screen for type 2 diabetes and diagnose gestational diabetes, a type of diabetes that develops during pregnancy. The test is conducted in several steps: first, a fasting blood glucose level is measured; then, the individual consumes a glucose solution containing sugar; and finally, blood glucose levels are tested again after a specified period, usually one, two, or three hours. Results are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). The test helps identify abnormalities in how your body handles glucose after a meal, often before your fasting blood glucose level becomes abnormal.
What is Glucose Tolerance Test used for?
The glucose tolerance test is used to screen for type 2 diabetes and to diagnose gestational diabetes during pregnancy. It measures the body's response to sugar (glucose) and identifies abnormalities in the way the body handles glucose after a meal. The test results can indicate impaired glucose tolerance (prediabetes), type 2 diabetes, or a normal glucose level. It is important to eat and drink normally in the days leading up to the test and to fast for eight hours before the test. The glucose tolerance test involves drinking a glucose solution and having blood glucose levels measured periodically afterward.
How to prepare for Glucose Tolerance Test?
Before the glucose tolerance test, it's important to eat and drink normally in the days leading up to the test. Inform your doctor if you're ill or taking any medications, as these factors can affect the test results. Eight hours before the test, you won't be able to eat or drink anything. It may be helpful to fast overnight and schedule the test for early the following morning. During the test, a healthcare professional will take a blood sample from a vein in your arm to measure your fasting blood glucose level. Then, you'll be asked to drink a syrupy glucose solution containing a specific amount of sugar. Your blood glucose level will be tested again after a set time period (either one or two hours for a regular glucose tolerance test, or one, two, and three hours for a three-hour glucose tolerance test). After completing the test, you can return to your usual activities immediately. Remember to follow your healthcare provider's specific instructions regarding preparation and timing for your glucose tolerance test.
How is Glucose Tolerance Test conducted?
An oral glucose tolerance test (OGTT) is conducted to measure the body's response to sugar (glucose). For type 2 diabetes screening or gestational diabetes diagnosis, a modified version of the OGTT is performed. For the one-hour test, after an overnight fast, a blood sample is taken, and then the individual drinks a glucose solution. One hour later, another blood sample is taken and tested for glucose levels. If the results are suspicious, a three-hour glucose tolerance test may be recommended. For the three-hour test, the individual is asked to come fasting and a blood sample is taken. Then, they drink a glucose solution, and blood glucose levels are measured one, two, and three hours later. In both tests, it's essential to eat and drink normally in the days leading up to the test, and inform the doctor about medications or illnesses that may affect the results.
How are Glucose Tolerance Test results reported?
Glucose tolerance test results are reported in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). A normal blood glucose level after two hours of drinking the glucose solution is lower than 140 mg/dL (7.8 mmol/L). A blood glucose level between 140 and 199 mg/dL (7.8 and 11 mmol/L) is considered impaired glucose tolerance or prediabetes. A blood glucose level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes. If the results indicate type 2 diabetes, your doctor may repeat the test on another day or use another blood test to confirm the diagnosis.
Understanding the report
Glucose tolerance test results are interpreted based on the measurements taken one hour, two hours, and three hours after consuming a glucose solution. For a one-hour test, if the blood glucose level is 200 mg/dL (11.1 mmol/L) or higher, it may indicate diabetes. For a two-hour test during screening for type 2 diabetes, a blood glucose level between 140 and 199 mg/dL (7.8 and 11 mmol/L) is considered impaired glucose tolerance or prediabetes. For a three-hour test, a normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L) at all three hours. If the results indicate abnormalities, your doctor may repeat the test on another day or use another blood test to confirm the diagnosis. Various factors can affect the accuracy of the glucose tolerance test, including illness, activity level, and certain medications.
Limitations and Considerations
The glucose tolerance test is a reliable method for screening for type 2 diabetes and gestational diabetes. However, there are some limitations to consider: 1. Accuracy can be affected by factors such as illness, certain medications, and physical activity levels. In such cases, your doctor may recommend a three-hour glucose tolerance test for a more accurate assessment. 2. The test only provides information about your body's response to glucose at a specific point in time. It does not indicate how your body will respond to glucose over a longer period. 3. The test requires you to fast for eight hours beforehand, which may not be practical or comfortable for some individuals, especially children. 4. Some people may experience adverse reactions to the glucose solution, such as nausea, vomiting, or abdominal discomfort. It is essential to discuss any concerns or questions you have with your healthcare provider before undergoing the glucose tolerance test. They can help determine if the test is appropriate for your specific situation and provide guidance on how to prepare and interpret the results.