A glucose tolerance test (GTT) is a medical assessment that determines how efficiently your body processes glucose, a type of sugar and primary energy source. This test measures how well your body moves sugar from the bloodstream into tissues like muscle and fat. It is a common diagnostic tool used to screen for conditions such as prediabetes, type 2 diabetes, and gestational diabetes, which occurs during pregnancy.
Preparing for Your Glucose Tolerance Test
Preparing correctly for a glucose tolerance test is important for accurate results. In the days leading up to the test, maintain your usual diet, consuming at least 150 grams of carbohydrates daily for at least three days. This prepares your body for the glucose challenge. Discuss any medications or supplements with your healthcare provider, as some can affect blood sugar levels and may need adjustment.
Avoid strenuous physical activity for at least three days before the test, as intense exercise can influence glucose levels. The night before, fast for 8 to 14 hours, consuming only plain water. Fasting longer than 10 hours might cause your body to produce its own sugar, affecting results. On the test day, wear comfortable clothing and consider bringing quiet entertainment, as there will be a waiting period.
Steps of the Glucose Tolerance Test
The glucose tolerance test typically begins in the morning, often between 7:00 and 9:00 a.m. A healthcare professional takes an initial blood sample from your arm. This sample measures your fasting blood glucose level, establishing a baseline before any glucose is consumed.
Following this initial draw, you will drink a specific glucose solution. For adults, this usually contains 75 grams of glucose dissolved in 250 to 300 milliliters of water. You must consume the entire drink within a short timeframe, typically five minutes. Many describe the taste as very sweet, similar to a very sweet sports drink or flat soda.
After drinking the solution, you will enter a waiting period, remaining sedentary and avoiding eating, smoking, or drinking anything other than plain water. This allows your body to process the glucose. Healthcare professionals will take additional blood samples at timed intervals to monitor how your blood glucose levels change. For a standard test, samples are commonly drawn at one and two hours after consuming the drink, though some tests, particularly for gestational diabetes, may include draws at three hours. The entire procedure, from the first blood draw to the last, can take approximately two to three hours.
After the Test: What to Expect
Once the final blood sample is collected, you are typically free to leave the testing facility. Some individuals may experience mild side effects immediately after the test, such as nausea, dizziness, or lightheadedness, often due to the fasting and the sweet glucose drink. Eating a light meal or snack soon after can help alleviate these feelings.
The collected blood samples are sent to a laboratory for analysis to measure glucose levels. While turnaround time can vary, results are often processed within one to two business days. Some patients may receive results through an online health portal as early as the next morning. Your healthcare provider will review and interpret these results, discussing any findings and outlining next steps or follow-up care.