From the Guidelines
Patients should fast for at least 8 hours prior to a 1-hour GTT study. This recommendation is based on the most recent and highest quality study available, which defines fasting as no caloric intake for at least 8 hours 1. The fasting period is necessary to ensure the stomach is empty, providing clearer imaging results and preventing food from interfering with the transit of the radioactive marker or contrast material through the digestive system.
Key Considerations
- Fasting for at least 8 hours reduces the risk of aspiration if sedation is used during the GTT study.
- An empty stomach is essential for accurate imaging results, as food can interfere with the transit of the radioactive marker or contrast material.
- Some facilities may have specific protocols that vary slightly, so it's always best to follow the exact instructions provided by your healthcare provider or the imaging facility where your GTT study will be performed.
Evidence Summary
- The 2019 standards of medical care for type 2 diabetes in China define fasting as no caloric intake for at least 8 hours 1.
- Similar definitions of fasting are provided in other studies, including the 2010 standards of medical care in diabetes 1 and the 2014 executive summary of standards of medical care in diabetes 1.
- However, the 2019 study is the most recent and highest quality study available, and its definition of fasting should be prioritized.
Clinical Implications
- Patients should stop eating and drinking (except for small sips of water with medications if needed) at least 8 hours before the GTT study.
- If the test is scheduled in the morning, patients should fast overnight. If the test is scheduled in the afternoon, patients should have an early light breakfast and then fast for at least 8 hours before the test.
From the Research
Fasting Prior to 1-Hour Glucose Tolerance Test (GTT)
- The studies provided do not directly address the question of how long to fast prior to a 1-hour GTT 2, 3, 4, 5, 6.
- However, it is common practice to fast for at least 8 hours before an oral glucose tolerance test, including a 1-hour GTT, to ensure accurate results.
- The American Diabetes Association recommends an overnight fast of at least 8 hours before an oral glucose tolerance test 2.
- It is essential to note that the specific fasting period may vary depending on the individual's health status, age, and other factors, and should be determined by a healthcare professional.
- The provided studies focus on the accuracy of 1-hour plasma glucose during the oral glucose tolerance test in diagnosing type 2 diabetes 2, 6, alternative methods for diagnosing diabetes 3, and the impact of analytical and biological variations on diabetes classification 4, but do not provide information on the optimal fasting period before a 1-hour GTT.