Oral Glucose Tolerance Test (OGTT) Procedure
Jul 06, 2021
Source: Cainiu Health
Dr. Zhang Nan
Introduction
1. Objective: To determine whether the pregnant woman has gestational diabetes mellitus (GDM). Prior to the test, the participant must maintain a normal diet for three consecutive days before the examination.
2. Testing Method: A total of three blood samples are required—drawn in the fasting state, one hour after glucose ingestion, and two hours after glucose ingestion.
3. Procedure: On the day of the test, fasting blood is drawn between 7:00 AM and 9:00 AM; wearing loose-fitting clothing is recommended.
The oral glucose tolerance test (OGTT), also known as the glucose tolerance test, is a laboratory diagnostic method for diabetes. There are two main types: intravenous and oral. The intravenous glucose tolerance test (IVGTT) is suitable for special patients—such as those who have undergone gastrectomy or suffer from malabsorption syndromes—whereas the oral glucose tolerance test is the most commonly used clinical diagnostic tool. So, what are the procedural steps involved in an oral glucose tolerance test? Below, we address this question.
Steps of the Oral Glucose Tolerance Test (OGTT)
1. Clarify the Purpose
To determine whether a pregnant woman has gestational diabetes. Prior to the test, proper preparation is essential: for three consecutive days before testing, the subject must maintain a normal diet containing at least 150 g of carbohydrates per day and continue regular physical activity. Fasting (no food or drink) must begin after 10 p.m. the night before the test. Additionally, 75 g of anhydrous glucose powder should be prepared in advance for use during the test.
2. Testing Procedure
Blood samples are drawn three times: once in the fasting state, then again one hour and two hours after ingestion of the glucose solution. Therefore, subjects must consume a normal diet for the three days preceding the test. To ensure diagnostic accuracy, subjects must not deliberately restrict caloric intake prior to testing; dietary habits should remain unchanged for the preceding 72 hours.
3. Detailed Testing Steps
On the day of the test, a fasting blood sample is drawn between 7:00 a.m. and 9:00 a.m. Wearing loose-fitting clothing is recommended to facilitate venipuncture. After blood collection, dissolve 75 g of glucose powder in 300 mL of warm boiled water, stir thoroughly, and consume the entire solution within five minutes. Timing begins with the first sip of the glucose solution.
Additional Information: Important Considerations for the Glucose Tolerance Test
1. Before the Test
Maintain emotional stability and avoid vigorous physical activity. To ensure accurate results, pregnant women should refrain from excessive exercise before the test and strive to remain calm. Fasting is mandatory for at least 12 hours prior to the test—no food, water, beverages, or coffee may be consumed, to ensure that the true fasting plasma glucose level is reflected.
2. During the Test
Pregnant women must not eat or smoke during the test but may walk gently. It is important to remain relaxed and avoid anxiety while patiently cooperating with healthcare providers during evaluation. Should nausea, pallor, dizziness, or syncope occur during the test, immediate medical assistance must be sought.
3. After the Test
Reference values for each time point are derived from statistical analysis of large population samples. However, due to technical limitations and individual physiological variations, OGTT results may contain some degree of measurement error.
The above outlines the procedural steps for the oral glucose tolerance test. We hope this information proves helpful.
