Does water intake before or after the Oral Glucose Tolerance Test (OGTT) affect the results?

From the Guidelines

Drinking water before or after taking a glucose tolerance test does not significantly affect the results, and moderate water intake is actually beneficial for ensuring good blood flow and accurate glucose readings. When taking a GTT, it is essential to follow the specific instructions provided by your healthcare provider. According to the guidelines on diabetes, pre-diabetes, and cardiovascular diseases by the European Society of Cardiology (ESC) and the European Association for the Study of Diabetes (EASD) 1, the optimal way to take a GTT involves fasting for 8-14 hours beforehand, typically overnight, and then consuming a glucose solution containing 75g of glucose dissolved in 250-300 mL of water.

The key aspects to consider when taking a GTT include:

• Fasting for 8-14 hours before the test
• Avoiding smoking, caffeine, and exercise on the morning of the test
• Remaining seated or resting during the entire testing period
• Drinking the glucose solution within 5 minutes, as specified in the guidelines 1
• Providing blood samples at specific intervals, usually at 1 hour and 2 hours after consuming the glucose solution

It is also important to note that dehydration can potentially lead to falsely elevated glucose readings, while moderate water intake can help ensure good blood flow for easier blood draws. Therefore, drinking plain water in moderate amounts during the fasting period and while waiting between blood draws is generally allowed and does not significantly affect the results. However, it is crucial to follow the specific instructions provided by your healthcare provider to ensure accurate and reliable results.

From the Research

Effect of Drinking Water on Glucose Tolerance Test Results

• There is no direct evidence in the provided studies to suggest that drinking water before or after taking a glucose tolerance test (GTT) affects the results 2, 3, 4, 5, 6.
• The studies focus on the oral glucose tolerance test (OGTT) as a diagnostic tool for detecting prediabetes and type 2 diabetes, and the factors that influence its accuracy, such as fasting plasma glucose (FPG), 2-hour post-load glucose (2-h PG), and HbA1c levels 3, 4, 5, 6.

Optimal Way to Take the GTT

• The optimal way to take the GTT is not explicitly stated in the provided studies, but it is generally recommended to follow a standardized protocol, such as fasting for 10-12 hours before the test and consuming a glucose solution containing 75g of glucose 2, 3, 4.
• The studies suggest that the GTT is a reliable diagnostic tool for detecting diabetes and impaired glucose tolerance, and that it can provide valuable information on insulin release and insulin sensitivity 3, 5.
• The use of demographic parameters and values obtained during the OGTT, such as BMI, waist-to-hip ratio, and plasma glucose and insulin levels, can help predict insulin sensitivity and insulin release with reasonable accuracy 3.

Factors that Influence GTT Results

• Factors that can influence GTT results include fasting plasma glucose levels, 2-hour post-load glucose levels, and HbA1c levels 4, 5, 6.
• The studies suggest that the GTT is a more accurate diagnostic tool than FPG or HbA1c alone, and that it can help identify individuals with diabetes or impaired glucose tolerance who may be misclassified using other diagnostic criteria 5, 6.