Your 75g Glucose Tolerance Test Results: What They Mean

Q: Your 75g Glucose Tolerance Test Results: What They Mean

Dear Ms. Huihui： 1. According to the American Diabetes Association's diagnostic criteria for diabetes： a. Fasting plasma glucose level ≥126 mg/dl after fasting for more than 8 hours. b. Plasma glucose level ≥200 mg/dl during a 2-hour oral glucose tolerance

75 grams oral glucose tolerance test?

Hello, I recently underwent a 75-gram oral glucose tolerance test after fasting for eight hours, and the results were as follows: Fasting: 75 mg/dL, 1 hour after drinking the glucose solution: 88 mg/dL, and 2 hours after drinking the glucose solution: 162 mg/dL.
Are these numbers normal? Why is there such a significant difference between the values at the 1-hour and 2-hour marks after drinking the glucose solution? Are these measurements reasonable, or do they have any special significance?

Huihui, 40~49 year old female. Ask Date: 2016/07/08

Dr. Xiao Yongxun reply Internal Medicine

Dear Ms.
Huihui:
1.
According to the American Diabetes Association's diagnostic criteria for diabetes: a.
Fasting plasma glucose level ≥126 mg/dl after fasting for more than 8 hours.
b.
Plasma glucose level ≥200 mg/dl during a 2-hour oral glucose tolerance test.
c.
HbA1c (glycated hemoglobin) ≥6.5% (must not have any disproportionate hyperglycemia, and the testing method must comply with the international certification standards of NGSP and DCCT).
The above criteria a, b, and c must be met on two separate occasions.
d.
Clinical symptoms of diabetes (such as polyuria, polydipsia, polyphagia, weight loss, etc.) with any plasma glucose level ≥200 mg/dl (this condition only needs to be met once).
2.
Generally, postprandial blood glucose levels gradually rise, reaching a peak two hours after eating, and then gradually decline.
If high-sugar or high-calorie foods are consumed and there is sufficient insulin secretion, blood glucose levels may spike rapidly; they may even peak one hour after eating before gradually declining.
The term "two hours postprandial" refers to two hours after the start of eating.
In clinical practice, for convenience in treatment or discussion, postprandial blood glucose levels at two hours are commonly used; fewer people use one-hour postprandial blood glucose levels as a standard for discussion or treatment.
Normal postprandial plasma glucose levels in healthy individuals are below 140 mg/dl, while those with impaired glucose tolerance have postprandial plasma glucose levels between 140 and 180 mg/dl.
If postprandial plasma glucose levels exceed 180 mg/dl, the risk of diabetes should be considered.
However, due to individual differences in food intake and timing, standardized glucose tolerance tests have been developed.
3.
In clinical medicine, various dosages and reference values for glucose tolerance tests for diabetes have been developed over the past 60 years.
In fact, metabolic specialists may not remember every testing method and dosage.
The most commonly used methods include 50 grams, 75 grams, and 100 grams of glucose; especially in the screening and diagnosis of gestational diabetes, different physicians may use different methods, with some using 50 grams and others using 75 grams.
Additionally, the timing of blood glucose measurements may vary.
However, these variations do not hinder practical clinical application, as the onset of diabetes is usually gradual and rarely occurs suddenly.
4.
You underwent a 75-gram glucose test after fasting for more than eight hours; your plasma glucose level was 88 mg/dl one hour after drinking the glucose solution, and 162 mg/dl two hours after.
The results are theoretically reasonable and normal.
As for "why is there such a large discrepancy between the first and second hour values?" the explanation in point 2 above is also reasonable.
5.
Your comprehensive testing indicates that your physician is very attentive and excellent; it would be advisable for you to discuss this thoroughly with your physician.
6.
Risk factors for developing diabetes include a family history of diabetes, obesity, hypertension, hyperlipidemia, lack of exercise, excessive eating, alcohol abuse, certain medications, poor lifestyle choices, and excessive stress; please pay close attention to these factors.

Reply Date: 2016/07/08

More Info

Understanding your 75g Glucose Tolerance Test (OGTT) results is crucial for assessing your glucose metabolism and potential risk for diabetes. Based on the results you provided—fasting blood glucose of 75 mg/dL, 1-hour post-glucose intake of 88 mg/dL, and 2-hour post-glucose intake of 162 mg/dL—let's break down what these numbers mean and why there might be a significant difference between the 1-hour and 2-hour readings.

Normal Ranges and Interpretation
1. Fasting Blood Glucose: A fasting blood glucose level of 75 mg/dL is considered normal. According to the American Diabetes Association, normal fasting glucose levels are below 100 mg/dL.
2. 1-Hour Post-Glucose Level: Your 1-hour post-glucose level of 88 mg/dL is also within the normal range. Typically, blood glucose levels should peak within the first hour after consuming glucose, but they should remain below 180 mg/dL for a normal response.

3. 2-Hour Post-Glucose Level: The 2-hour reading of 162 mg/dL is where the concern arises. While this value is below the 200 mg/dL threshold that indicates diabetes, it is above the normal range for glucose tolerance tests. A normal 2-hour post-glucose level should be less than 140 mg/dL. Values between 140 mg/dL and 199 mg/dL indicate impaired glucose tolerance, which is a risk factor for developing type 2 diabetes.

Understanding the Discrepancy
The significant difference between your 1-hour and 2-hour readings can be attributed to several factors:
- Physiological Response: After consuming glucose, your body should ideally release insulin to help lower blood sugar levels. In a healthy individual, blood sugar levels peak shortly after glucose intake and then decline as insulin facilitates glucose uptake by cells. Your 1-hour reading is low, suggesting that your body is initially responding well to the glucose load. However, the 2-hour reading indicates that your body may not be effectively managing glucose levels over time, which could suggest insulin resistance or impaired glucose metabolism.

- Insulin Sensitivity: If your body is not sensitive enough to insulin, it may struggle to lower blood sugar levels effectively after the initial peak. This could explain why your 2-hour reading is elevated despite a normal 1-hour reading.

- Diet and Lifestyle Factors: Your diet, physical activity level, and overall health can influence how your body processes glucose. High carbohydrate intake, sedentary lifestyle, or stress can all impact your glucose metabolism.

Recommendations
Given your results, it would be prudent to discuss them with your healthcare provider. They may recommend:
- Further Testing: Additional tests, such as a repeat OGTT or an HbA1c test, can provide more insight into your glucose metabolism over time.

- Lifestyle Modifications: If you are at risk for developing diabetes, adopting a healthier lifestyle can be beneficial. This includes a balanced diet low in refined sugars and carbohydrates, regular physical activity, and maintaining a healthy weight.

- Monitoring: Regular monitoring of your blood glucose levels can help you and your healthcare provider track any changes and decide on the best course of action.

Conclusion
In summary, while your fasting and 1-hour glucose levels are normal, the 2-hour level indicates a potential issue with glucose tolerance. This discrepancy highlights the importance of monitoring and possibly adjusting your lifestyle to mitigate the risk of developing diabetes. Always consult with your healthcare provider for personalized advice and recommendations based on your specific health needs.

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