Blood Sugar Monitoring: Accuracy and Common Concerns

Q: Blood Sugar Monitoring: Accuracy and Common Concerns

Hello： The blood glucose levels obtained from a standard blood draw are typically about 15% higher than those measured by a glucose meter, which may raise some questions for you. <br>Since you are at high risk for diabetes, it is recommended that you continue to manage your diet

About diabetes?

First of all, I would like to thank Dr.
Lee for the previous response.
I do have hyperlipidemia and hypertension, which I am currently managing with medication.
My average blood pressure is (systolic) 110-120 and (diastolic) 65-75.
In my last inquiry, my fasting blood glucose was 117, and my hemoglobin A1c was 5.8, with triglycerides at 193.
After that, I started measuring my blood glucose levels periodically with a glucometer, and here are the readings: on May 8th, fasting in the morning was 84; on May 9th, two hours after lunch it was 91; on May 11th, fasting in the morning was 87; on May 17th, four hours after lunch it was 78; and on May 23rd, two hours after breakfast it was 89.
I am wondering why these readings differ significantly from the blood test results at the hospital.
I once called the manufacturer to inquire if the glucometer was inaccurate, and they responded that every glucometer has a margin of error and cannot be 100% accurate, and that my blood glucose data falls within the normal range of error.
I would like to ask Dr.
Lee if the manufacturer's statement is correct or if I might be measuring my blood glucose incorrectly.
Thank you, Doctor, for taking the time to respond.

Dadi Shu, 40~49 year old female. Ask Date: 2012/05/24

Dr. Li Zhiyao reply Internal Medicine

Hello: The blood glucose levels obtained from a standard blood draw are typically about 15% higher than those measured by a glucose meter, which may raise some questions for you.
Since you are at high risk for diabetes, it is recommended that you continue to manage your diet and engage in appropriate exercise while avoiding obesity or being overweight.
If you have habits such as smoking, drinking alcohol, or chewing betel nut, it is advisable to quit as soon as possible.
It is suggested to monitor your blood glucose, hemoglobin A1c, triglycerides, and cholesterol levels every 3 to 6 months to detect any abnormalities early.
Thank you for your inquiry, and I wish you good health!

Reply Date: 2012/05/24

More Info

Thank you for your question regarding blood sugar monitoring and the discrepancies you’ve observed between your home glucose meter readings and laboratory results. It’s great to hear that you are actively managing your health conditions, including hyperlipidemia and hypertension. Let’s delve into the accuracy of blood sugar monitoring and address your concerns.

Understanding Blood Sugar Monitoring
1. Differences Between Home Glucose Meters and Laboratory Tests:
Home glucose meters measure blood sugar levels using a small drop of blood, typically obtained by pricking a fingertip. This measurement reflects the glucose concentration in whole blood. In contrast, laboratory tests often analyze plasma glucose, which is the liquid component of blood after cells have been removed. Plasma glucose levels are generally higher than whole blood glucose levels due to the dilution effect of the plasma. This difference can lead to variations in readings between home meters and lab tests.

2. Accuracy of Home Glucose Meters:
It is true that every glucose meter has a margin of error, which can be influenced by several factors, including the specific model of the meter, the calibration of the device, and even the technique used during testing. The FDA allows a 15% variance for glucose meters, meaning that a reading of 100 mg/dL could actually be anywhere from 85 to 115 mg/dL. Therefore, your readings may fall within an acceptable range of error, but it’s essential to ensure that your meter is calibrated correctly and that you are using it according to the manufacturer’s instructions.

3. Factors Affecting Blood Sugar Readings:
Several factors can affect the accuracy of your readings:
- Timing of the Test: Blood sugar levels fluctuate throughout the day based on food intake, physical activity, and other factors. Testing at different times can yield different results.

- Technique: Ensure that you are using proper technique when obtaining your blood sample. This includes washing your hands, using a fresh test strip, and following the meter’s instructions closely.

- Meter Maintenance: Regularly check the expiration dates on test strips and ensure that the meter is clean and functioning properly.

4. Interpreting Your Readings:
Your reported readings of 84.5, 87.5, and 91.5 mg/dL are all within the normal range for fasting blood glucose levels, which is typically below 100 mg/dL. The readings you obtained after meals (e.g., 91.5 two hours after lunch) also indicate good glucose control, as postprandial (after meal) blood sugar levels should ideally be below 140 mg/dL.

5. Consulting with Your Healthcare Provider:
Given your history of high blood pressure and hyperlipidemia, it’s crucial to maintain regular communication with your healthcare provider. They can help you interpret your blood sugar readings in the context of your overall health and may recommend periodic laboratory tests to confirm your home monitoring results. If you notice any significant discrepancies or if your symptoms change, it’s important to seek medical advice.

Conclusion
In summary, while home glucose meters are a useful tool for monitoring blood sugar levels, they are not infallible. Variations between home and lab results can occur due to differences in measurement techniques and inherent inaccuracies in the devices. It’s essential to use your glucose meter correctly and to maintain regular check-ups with your healthcare provider to ensure that your blood sugar levels remain within a healthy range. If you have further concerns about your readings or your health, don’t hesitate to reach out to your doctor for personalized advice and management strategies.

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