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Glucose measurement is one of the earliest and most frequently performed tests in the clinical laboratory. This service is most often used by patients with diabetes. Despite the existence of reference standards, the determination of blood glucose can be an extremely complex test and, in some cases, give approximate results. This is because different methods analyze the glucose present in different fractions of a blood sample. They may use different analytical principles and also express results differently. Glucose is available for measurement in any blood fraction such as plasma or whole blood. Accurate measurement is important for people with diabetes. There are many devices for this, but a glucometer is one of the fastest and most effective options.
What is a glucometer
A glucometer is a special device that can measure the presence of glucose in the blood. The result is sent to the device screen within a few seconds. Although the measurement of sugar levels is usually performed in the laboratory, the use of a whole blood sample introduces complications and inaccuracies in terms of the principle of analysis, the method of calibration, and the expression of results. Most glucometers are calibrated to a method chosen by the manufacturer for reference purposes, so it is expected that blood samples from different individuals will not necessarily behave similarly (whether in comparison methods or treatments).
While most conventional laboratory methods measure glucose as a concentration in plasma or whole blood, direct-reading glucometers measure it in mmol/kg of water, which is numerically larger, but the results are often factorized and expressed, for example, as plasma glucose concentration.
However, there is inconsistency and difference in the methods and principles of measurement, which leads to some difficulties in comparing blood glucose results obtained by different devices. It has been suggested that some uncertainty can be removed by expressing all results as plasma glucose concentration, regardless of sample type or analytical method used. Variation in the site of blood sampling can also lead to errors, especially when testing with spot treatment. This means that the glucometer has both its advantages and some disadvantages.
Classification of glucometers and methods of blood analysis
Several options for checking blood are used, which depend on the device itself. The quality of chemical analysis is relatively higher, so an electric glucometer is not suitable for diagnosing diabetes. In addition, the probability of getting errors is too high. An electronic device is more suitable for measuring glucose levels and monitoring them on a daily basis. There are several methods:
- chemical (plasma measurement);
- chemical (whole blood measurement);
- electronic (photometric, electrochemical, biosensor glucometers);
- physical (infrared lamp).
Currently, chemical methods for analyzing blood glucose invariably rely on methods involving enzymes (e.g., glucose oxidase, glucose dehydrogenase, hexokinase, etc.) associated with chromogenic reactions or reactions with changes in electron flow, which can also be measured using suitable electronic meters. There are techniques using physical methods for detecting glucose, such as infrared, that are less widely available.
However, not all blood sugar tests measure the same thing. Laboratory methods using plasma (homogeneous liquid) usually agree well because they respond to glucose dissolved in the entire volume of the sample, and the results are expressed as the concentration of glucose per unit volume of plasma, for example, in mmol/L. For methods using whole blood, the situation is more complicated and partly depends on whether the first sample was hemolyzed or the blood sample was diluted prior to measurement. Red blood cells and plasma contain different amounts of dissolved solids such as proteins, and therefore have different proportions of water per unit volume, the water content of the volume of red blood cells is lower than the same volume of plasma.
The effectiveness of modern glucometers
Although the principle of the method is an important determinant of the final result of the analysis, calibration is equally or even more important. Some testing methods are much more effective than a glucometer, but device manufacturers usually set up their systems so that a blood sample will give about the same result on the analyzer as their chosen “reference” method.
This assumes that all samples have similar characteristics, meaning that a given method will respond the same way under all circumstances. In practice, this is not always the case. For example, an assay may give the same result for an average hematocrit sample as a reference method, but may diverge when the hematocrit is high or low due to the separate and additive effects of different distribution of water in different blood fractions. According to statistics, an electric glucometer gives a deviation in the result by about 20%.
How to determine the result of a blood test
How should the results be expressed? There is a legitimate argument that glucose results should be expressed in terms of sample activity in water (considered the same for plasma and erythrocytes), as this represents the glucose available in tissues. However, most modern laboratory methods do not directly measure this, let alone glucometers. Instead, they look at and analyze the plasma concentration, which is numerically lower, and that is how they express their results.
For methods using a whole blood sample, the result is often, but not always, expressed as the concentration of whole blood glucose, which gives a figure lower than for plasma glucose. In truth, none of these are entirely correct, as some analyzes will be affected by the presence of varying numbers of RBCs in the samples.
Even direct reading electrodes typically factorize readings to express them under normal concentration conditions rather than as actual activity measured, and it has been suggested that all methods report plasma glucose concentration to avoid confusion, no matter what type of sample or method. measurements.
Therefore, glucometer manufacturers must make assumptions about the average number of red blood cells in a blood sample, knowing that deviations from this will lead to some error. However, it is important to understand that a method that accepts a whole blood sample cannot express results in a certain way without carefully checking the manufacturer’s instructions. Accordingly, it is necessary to study the instructions for the device to determine the exact results, since each manufacturer has an individual mechanism and the testing error may be to a lesser or greater extent.
Guided by the result, the patient can independently adjust his menu, since carbohydrates most often affect glucose levels. A diabetic person should avoid or limit certain foods. New glucometers do not pose a need to go to the doctor for a decoding of the result. The patient will be able to decrypt at home according to special instructions.