the Discrepancy Between Blood Glucose Meter and Lab Results

Q: the Discrepancy Between Blood Glucose Meter and Lab Results

Dear Ms. Wang Su-Chen： 1. According to the diagnostic criteria for diabetes set by the American Diabetes Association, a. a fasting plasma glucose level of ≥126 mg/dL after fasting for more than 8 hours, b. a 2-hour plasma glucose level of ≥200 mg/dL during an o

Questions about blood glucose meters?

Hello Doctor: Recently, a family member noticed that urination attracted ants, so they went to the clinic for a blood test.
On the same day, after the nurse drew blood, she used the venous blood to measure fasting blood glucose with a Roche Accu-Chek glucose meter, which showed a value of 167 mg/dL.
A few days later, the blood test report indicated a fasting blood glucose level of 267 mg/dL and an HbA1c of 10.58%.
Could you please explain why there is such a significant difference between the glucose meter reading and the plasma glucose value? Can this result be used to diagnose diabetes? Thank you for your time, and I wish you good health.

Wang Su-Zhen, 40~49 year old female. Ask Date: 2017/09/01

Dr. Xiao Yongxun reply Internal Medicine

Dear Ms.
Wang Su-Chen:
1.
According to the diagnostic criteria for diabetes set by the American Diabetes Association, a.
a fasting plasma glucose level of ≥126 mg/dL after fasting for more than 8 hours, b.
a 2-hour plasma glucose level of ≥200 mg/dL during an oral glucose tolerance test, c.
a hemoglobin A1c (HbA1c) of ≥6.5% (this must be confirmed by a method that is certified by the National Glycohemoglobin Standardization Program (NGSP) and meets the Diabetes Control and Complications Trial (DCCT) standards).
The above criteria a, b, and c must be confirmed by two separate tests.
d.
If there are clinical symptoms of diabetes (such as polydipsia, polyuria, polyphagia, weight loss, etc.), and any plasma glucose level is ≥200 mg/dL, then only one test is required for diagnosis.
2.
It is possible for there to be discrepancies between blood glucose values obtained from a glucose meter and those obtained from laboratory tests.
Blood glucose measured by a fingerstick typically reflects whole blood glucose in microcapillaries, while laboratory tests measure plasma glucose obtained through centrifugation, which is generally considered more reliable.
Therefore, your plasma glucose level is 267 mg/dL, and your HbA1c level is 10.58%.
There is a strong suspicion of diabetes (in fact, the fasting glucose reading from the glucose meter is 167 mg/dL, which is clearly elevated).
However, it is still advisable to discuss this with your physician, as clinical symptoms and other factors must also be considered for a definitive diagnosis.
3.
As for general glucose meters, they are indeed less accurate than plasma glucose measurements.
It is possible that the glucose meter has not been calibrated for a long time; however, medical facilities often have their glucose meters regularly calibrated by manufacturers, so it remains uncertain whether the issue lies with the glucose meter.
Additionally, factors such as hemoglobin A1c, triglycerides, and electrolytes in the blood may also affect the readings from the glucose meter.
It is recommended that you discuss this issue with your attending physician for appropriate clarification.
4.
In clinical practice, many experienced physicians may make a diagnosis of diabetes during the initial examination based on limited information and experience, in order to initiate prompt management and prevent acute complications that could lead to emergency department visits or intensive care unit admissions.

Reply Date: 2017/09/01

More Info

The discrepancy between blood glucose meter readings and laboratory results can be attributed to several factors, and understanding these differences is crucial for accurate diabetes management. In your case, the blood glucose meter indicated a fasting blood sugar level of 167 mg/dL, while the laboratory test reported a fasting blood sugar level of 267 mg/dL. Additionally, your HbA1c level was recorded at 10.58%, which is indicative of poorly controlled diabetes.

Factors Contributing to Discrepancy
1. Measurement Techniques: Blood glucose meters typically measure whole blood glucose levels, while laboratory tests often measure plasma glucose levels. Plasma glucose levels are generally higher than whole blood glucose levels due to the concentration of glucose in plasma. This difference can lead to discrepancies in readings.

2. Calibration and Accuracy: Blood glucose meters require regular calibration to ensure accuracy. If the meter is not calibrated correctly or if it has been used for an extended period without maintenance, the readings may be inaccurate. Additionally, different brands and models of glucose meters may have varying degrees of accuracy.

3. Sample Handling: The way blood samples are handled can also affect glucose readings. For instance, if the blood sample is not processed quickly enough, glucose levels can decrease due to glycolysis (the breakdown of glucose by cells). Laboratory tests are typically performed under controlled conditions, which can yield more reliable results.

4. Physiological Factors: Factors such as dehydration, stress, or recent physical activity can affect blood glucose levels. If the blood glucose meter was used shortly after eating or during a period of stress, it might not reflect the true fasting glucose level.

5. User Error: The accuracy of home glucose meters can also be influenced by user error, such as improper technique in blood sampling or not following the manufacturer's instructions.

Diagnosis of Diabetes
Based on the laboratory results you provided, particularly the fasting blood glucose level of 267 mg/dL and the HbA1c of 10.58%, it is reasonable to conclude that you meet the criteria for a diagnosis of diabetes. According to the American Diabetes Association (ADA), the diagnostic criteria for diabetes include:
- Fasting plasma glucose (FPG) ≥ 126 mg/dL (7.0 mmol/L)
- 2-hour plasma glucose ≥ 200 mg/dL (11.1 mmol/L) during an Oral Glucose Tolerance Test (OGTT)
- A1c ≥ 6.5% (48 mmol/mol)
- Random plasma glucose ≥ 200 mg/dL (11.1 mmol/L) in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis
Given that your fasting glucose and HbA1c levels exceed these thresholds, it is advisable to consult with your healthcare provider for a comprehensive evaluation and to discuss a management plan tailored to your needs.

Next Steps
1. Consult Your Healthcare Provider: It is essential to discuss these results with your healthcare provider, who can interpret them in the context of your overall health and medical history.

2. Regular Monitoring: If diagnosed with diabetes, regular monitoring of blood glucose levels is crucial. This includes both home monitoring and periodic laboratory tests to assess long-term glucose control.

3. Lifestyle Modifications: Implementing dietary changes, increasing physical activity, and possibly starting medication can help manage blood glucose levels effectively.

4. Education: Understanding diabetes management, including how to use your blood glucose meter correctly and recognizing the signs of high or low blood sugar, is vital for effective self-care.

In summary, the discrepancies between your blood glucose meter and laboratory results can stem from various factors, and your laboratory results indicate a diagnosis of diabetes. It is crucial to work closely with your healthcare provider to develop a management plan that addresses your specific needs.

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