Is Your Blood Sugar Test Accurate? Post-Meal Readings

Q: Is Your Blood Sugar Test Accurate? Post-Meal Readings

Dear Mr. Cheng： 1. Blood consists of approximately 55% blood cells and 45% plasma. During circulation, some plasma can seep into the interstitial spaces, mixing with the secretions of tissue cells to form interstitial fluid. Therefore, the concern you have rega

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Hello, doctor.
Continuing from my previous question, that night I felt anxious and restless.
After having dinner, about two hours later, I went to one of the clinics to self-pay for a blood glucose test.
The nurse cleaned my finger with alcohol and shortly after, she pricked my finger.
However, there wasn't much blood.
She squeezed my fingertip to get enough blood for the test, which resulted in a reading of 92.
The doctor looked at it and said it was normal and told me not to worry.
At that moment, I felt reassured that I was fine.
However, when I got home, I realized that the squeezing of the wound during the test might have caused interstitial fluid to dilute the blood glucose.
What if I actually exceeded the standard? What should I do if the nurse's squeezing of my finger led to an inaccurate test result? I know that two hours after a meal, the level should be below 140.
So, is the reading of 92 reliable?

Cheng Cheng, 20~29 year old female. Ask Date: 2017/05/27

Dr. Xiao Yongxun reply Internal Medicine

Dear Mr.
Cheng:
1.
Blood consists of approximately 55% blood cells and 45% plasma.
During circulation, some plasma can seep into the interstitial spaces, mixing with the secretions of tissue cells to form interstitial fluid.
Therefore, the concern you have regarding the dilution of interstitial fluid is rarely mentioned in the context of microvascular blood glucose testing.
This is because diabetes blood glucose detection primarily checks plasma glucose levels.
Of course, red blood cells, white blood cells, and platelets theoretically contain a small amount of glucose, but this has a minimal impact compared to plasma glucose levels.
Similarly, when interstitial fluid first seeps from the microvasculature, its glucose concentration is comparable to that of plasma, and it also has a negligible effect.
2.
It is standard practice for nurses to use a lancet and apply pressure to facilitate blood flow; this helps minimize blood loss for the patient and reduces the pain associated with deeper punctures.
3.
Based on your description, your physician and nursing staff should be quite skilled and are interpreting the results correctly.
4.
If you still have doubts, you can opt for a blood draw to directly test plasma glucose levels instead of using a lancet for microvascular glucose testing.
However, this will incur higher costs and take more time.

Reply Date: 2017/05/27

More Info

When it comes to blood sugar testing, accuracy is paramount, especially for individuals concerned about diabetes or prediabetes. Your situation raises valid questions about the reliability of the reading you received, particularly given the circumstances surrounding the blood draw.

Firstly, it's essential to understand how blood sugar levels are measured and what factors can influence these readings. Blood glucose levels can fluctuate based on various factors, including the timing of the test in relation to meals, physical activity, stress, and even the method of blood collection.

In your case, you mentioned that the nurse had to apply pressure to your finger to obtain enough blood for the test. This practice can indeed introduce variables that may affect the accuracy of the reading. When pressure is applied, it can cause interstitial fluid (the fluid that surrounds cells) to mix with the blood sample. This dilution can lead to a lower reading than what might be accurate, especially if your blood sugar was elevated prior to the test.
The American Diabetes Association (ADA) states that a normal blood glucose level two hours after eating should be less than 140 mg/dL. Your reading of 92 mg/dL is well within the normal range, which is reassuring. However, if there were any concerns about the accuracy of the test due to the method of blood collection, it might be prudent to repeat the test under more controlled conditions.

For a more accurate assessment of your blood sugar levels, consider the following recommendations:
1. Timing of the Test: Ensure that the test is conducted at the appropriate time, ideally two hours after a meal, as you mentioned. This timing is crucial for understanding how your body processes glucose.

2. Method of Collection: If possible, opt for a venous blood draw rather than a fingerstick test. Venous blood samples are generally considered more reliable for glucose testing as they are less likely to be influenced by external factors like pressure.

3. Repeat Testing: If you have concerns about the accuracy of the reading, especially if you experience symptoms of high or low blood sugar, it may be wise to have your blood sugar tested again. You can also consider discussing continuous glucose monitoring with your healthcare provider for a more comprehensive view of your blood sugar levels over time.

4. Consult with Your Doctor: If you are still worried about your blood sugar levels or if you have a family history of diabetes, it’s essential to consult with your healthcare provider. They may recommend further testing, such as an HbA1c test, which provides an average blood sugar level over the past two to three months.

5. Lifestyle Factors: Regardless of the test results, maintaining a healthy lifestyle with balanced nutrition, regular physical activity, and stress management can significantly influence your blood sugar levels and overall health.

In conclusion, while your reading of 92 mg/dL is reassuring and falls within the normal range, the method of blood collection can impact the accuracy of the results. If you have any lingering doubts or symptoms, it’s always best to consult with your healthcare provider for further evaluation and guidance.

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