Many people when buying a new device for analyzing blood sugar after comparing its results with the indicators of previous devices notice the measurement error. Similarly, the numbers may have a different meaning if the study was conducted in a laboratory.
At first glance, it seems that all blood samples from the same person should have the same value when receiving indicators in the laboratory or home blood glucose meter. However, this is not the case; the point is that each equipment, whether specialized medical or for home use, has a different calibration, that is, a setting.
Therefore, the measurement of glucose in the blood occurs in different ways and the results of the analysis differ from each other. How big can be the error of blood glucose meters and which device is the most accurate, it is worth considering in more detail.
In order to understand how accurate the meter, you need to figure out what is such a thing as accuracy. According to medical data, home-blood sugar measurements are considered clinically accurate when they are in the range of ± 20 percent of a high-precision laboratory analyzer.
It is believed that this error meter does not have a significant impact on the treatment process, so it is valid for diabetics.
Also, before starting the data validation check, it is necessary to use the control solution, which is included in the device kit.
Difference with laboratory values
Most often, home devices conduct measurements of blood glucose in whole capillary blood, while laboratory equipment, as a rule, uses blood plasma for research. Plasma is a liquid component of the blood, obtained after the blood cells have settled and removed.
Thus, in the study of whole blood for sugar, the results are 12 percent lower than in plasma.
This means that in order to obtain reliable measurement data it is necessary to understand what the calibration of the meter and laboratory equipment is.
For diabetics, a special table has been developed, thanks to which it is possible to determine the difference between a conventional and a laboratory instrument, depending on what the calibration indicator is and what blood is being tested.
Based on this table, you can understand which analyzer should be compared with medical equipment, and which one does not make sense.
When using a capillary plasma laboratory, the comparison can be made as follows:
- If plasma is used during the analysis, the figures obtained will be almost identical.
- When conducting research on the glucometer for whole capillary blood, this result will be 12 percent lower than according to laboratory data.
- If plasma from a vein is used, a comparison can be made only if the diabetic is tested on an empty stomach.
- Whole venous blood in the blood glucose meter is not recommended for comparison, since the study should be carried out only on an empty stomach, and the data on the device will be 12 percent lower than laboratory values.
If the calibration of laboratory equipment is carried out by capillary blood, the results of the comparison may be completely different:
- When using plasma in the meter, the result will be 12 percent higher.
- Calibrating a home device for whole blood will have identical values.
- When the analysis is performed using venous blood, it is necessary to investigate on an empty stomach. At the same time, the figures will be 12 percent higher.
- When analyzing whole venous blood, the study is carried out exclusively on an empty stomach.
When conducting laboratory analysis using venous plasma, you can get the following results:
- A blood glucose meter calibrated to a plasma can only test on an empty stomach.
- When whole capillary blood is analyzed in a home device, the study can be carried out exclusively on an empty stomach. The result on the meter will be 12 percent lower.
- The ideal option for comparison is the analysis of venous plasma.
- When calibrating for whole venous blood, the result on the instrument will be 12 percent lower.
If a patient takes venous whole blood under laboratory conditions, the difference will be as follows:
- Glucometer calibrated with capillary plasma should be used only on an empty stomach, but in this case, these studies will be 12 percent higher.
- If a diabetic gives solid capillary blood, the comparison can only be done on an empty stomach.
- When they take venous plasma, the result on the meter is 12 percent higher.
- The best option is considered when venous whole blood is used at home.
How to compare the data
In order to obtain reliable indicators when comparing laboratory equipment and a conventional glucometer, it is necessary to consider how the device is calibrated. First of all, the laboratory data is transferred to the same measurement system as the standard device.
When calibrating the blood glucose meter for whole blood, and the laboratory analyzer for plasma, the indicators obtained in the clinic, must be mathematically divided by 1.12. So, upon receipt of 8 mmol / liter, after dividing the figure is 7.14 mmol / liter. If the meter shows numbers from 5.71 to 8.57 mmol / liter, which equates to 20 percent, the device can be considered accurate.
If the meter is calibrated for plasma, and whole blood is taken at the clinic, the laboratory results are multiplied by 1.12. When multiplying 8 mmol / liter, the indicator is 8.96 mmol / liter. The device can be considered properly working if the range of the obtained data is 7.17-10.75 mmol / liter.
When the calibration of equipment in the clinic and the usual device is carried out on the same sample, you do not need to convert the results. But it is important to remember that an error of 20 percent is allowed here. That is, when receiving the figure of 12.5 mmol / liter in the laboratory, the home blood glucose meter should give from 10 to 15 mmol / liter.
Despite the high error, which often scares, such a device is accurate.
Recommendations for determining the accuracy of the analyzer
In no case can you make a comparison of the analysis with the results of the study of other glucometers, even if they have a manufacturer of instruments. Each device is calibrated for a specific blood sample, which may not match.
When replacing the analyzer, be sure to notify the attending physician. It will help determine the range of blood sugar levels for the new device and, if necessary, make a correction in therapy.
During the acquisition of comparative data, the patient must ensure that the meter is clean. It is also important to ensure that the code matches the numbers on the test strips. After verification, testing is performed using a control solution. If this device gives indicators in the specified range, the meter is calibrated correctly. If a discrepancy is required, contact the manufacturer.
Before operating a new analyzer, find out which blood samples are used for calibration. Based on this, the measurement is calculated and the error is determined.
Four hours before the analysis of blood sugar is not recommended to eat. You also need to make sure that both samples for the meter and clinic were obtained at the same time. If venous blood is taken, the sample should be shaken thoroughly to allow mixing with oxygen.
It should be borne in mind that when vomiting, diarrhea, illness, as diabetic ketoacidosis and frequent urination, sweating strongly dehydrates the body. In this case, the meter may give inaccurate numbers that are not suitable for checking the accuracy of the instrument.
Before you take a blood sample, the patient must wash and rub his hands with a towel. It is impossible to use wet wipes and other foreign substances that can distort the result.
Since accuracy depends on the amount of blood received, it is necessary to warm the fingers with the help of a light massage of the hands and increase the blood flow. The puncture is done hard enough to allow the blood to flow freely from the finger.
Also on the market, relatively recently, blood glucose meters without test strips for home use have appeared. The video in this article will help you understand how the accuracy of the meter works.