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Philip Kern answered. Glucometer: The enzymatic reaction is glucose oxidase, and the reaction causes a color change that is read by the meter. Related questions A year-old member asked:. What is the best glucose meter? Is glucose meter accurate? Variation in hematocrit can cause serious errors in blood glucose when measured by SMBG.
Blood is composed of plasma and cells, and the percentage of red cells is the hematocrit. The red cells, however, are unusual among cells of the body in that they contain significant amounts of intracellular glucose. This variation is due solely to the altered contribution of the red cells to the whole blood value. Glucose in erythrocytes is in equilibrium with plasma glucose but at lower levels. The total blood glucose, therefore, is dependent on the hematocrit.
Most SMBG systems measure neither whole blood glucose nor plasma glucose, but rather a complex mixture, which is then calibrated against plasma glucose. Many meters use intricate systems to evaluate hematocrit and correct for it, but the effect of hematocrit is complex. Not only do the cells contain glucose at a different concentration than plasma, but the cells can block the electrode or the enzyme or alter the reading by a variety of other mechanisms.
Some meters, such as brand 2, in black, compensate well for changes in hematocrit or are not affected. Others, such as brand 1, shown in red, have excessive errors at low and high hematocrit levels.
Patient technique can play a significant role in the accuracy of blood glucose monitoring systems, but modern meters make it far easier for patients to get accurate results.
Over that period of time, the inaccuracy of the preprandial values fell from Over the decade of the s, meter accuracy did not improve when tested by highly trained nurses. In contrast, accuracy by the patient has improved significantly.
In , the accuracy of systems by patients using their own meters a wide variety , and by nurses, who had cleaned and calibrated the meters prior to taking a capillary sample from the patient, was evaluated. By , most patients were using biosensors with a capillary fill, and the average inaccuracy was approximately 7. In contrast, there was virtually no difference in the accuracy of the nurses and technicians between and yellow bars.
It appears that the systems did not necessarily become more accurate, but rather easier for patients to use appropriately. As seen in Figure 13 , when tested by nurses orange , meter accuracy did not improve substantially from to In contrast, accuracy did improve dramatically when tested by patients yellow.
Hand washing has always been a problem, but now, with microsample meters, the smallest amount of contaminant can significantly raise the blood glucose.
With a sample of 0. For example, one day when I came into work, the laboratory director met me at the door. She was very upset and complaining that our blood glucose meter must be inaccurate. We went to her office, where there was a banana peel sitting on her desk.
She had eaten the banana and then tested herself, without washing her hands. I had her wash her hands and test again. Keri lotion lowered the value slightly, and Ivory soap had no effect. Since patients generally do not wash their hands, this contamination can be a major source of inaccuracy. Sugary substances such as cookies Chips Ahoy raised glucose readings substantially. Lotions had only a minor effect and soap had almost none.
Some substances that occur naturally in the body can affect the accuracy of blood glucose monitoring. These substances are often present during certain disease states. Figure 6 shows the reaction that occurs on the SMBG strip. In electrochemical sensors, there are three locations that can be affected by both naturally occurring substances and by medications next section : 1 the interaction of glucose with the enzyme, 2 the transfer of electrons to the mediator from the enzyme, and 3 interactions at the electrode.
Three naturally occurring substances interfere with electrochemical glucose oxidase based strips: triglycerides, oxygen, and uric acid. Triglycerides, usually at very high levels, cause meters to be inaccurate because they take up volume, decreasing the amount of glucose in the capillary volume. Thus they cause values to be low. Oxygen, acting at location 2, competes with mediator to take electrons from the enzyme. Since strips are generally calibrated for capillary oxygen concentrations, high oxygen values, such as those found in arterial samples or in patients utilizing oxygen, will cause falsely lower values.
Finally, uric acid, though only at very high values, can be oxidized by the electrode location 3 , giving falsely high values.
Uric acid is seldom a problem, except in patients with values that would lead to severe gout. Glucose dehydrogenase is a less specific enzyme, so some naturally occurring sugars can compete with glucose at location 1. The monosaccharides, galactose, xylose, and the disaccharide maltose complete with glucose on glucose dehydrogenase and may give false values. Glucose dehydrogenase sensors, however, are less sensitive to variations in oxygen concentration.
A number of medications can alter the readings from SMBG. With electrochemical glucose oxidase systems, all seem to interact with the electrode location 3 and include acetaminophen, L-dopa, tolazamide, and ascorbic acid. With glucose dehydrogenase, other sugars can interfere. Maltose and xylose can have a small effect, but the most dangerous substance is icodextrin. Meter manufacturers have generally not disclosed and educated patients on the effects of interfering substances on their specific product.
Doing so would help patients to become more accurate in their measurements and therapeutic responses. Meters can be arbitrarily divided into three classes. The best of the meters have inaccuracies of 5. The values for any specific meter are not readily available, but most companies have tested their systems, know their accuracy, and can provide both the inaccuracy and the ISO numbers as described earlier. Generally, this is a bad idea. To receive a synopsis of a protocol to do testing in your site, send a request to moc.
Many centers are not equipped to test the meters properly and will obtain unreliable results. Proper testing requires a large number of patients usually at least 50, with — tests , a standardized protocol, and an acceptable capillary reference device such as a Yellow Spring Instruments or Beckman analyzer.
Comparing one meter to another is not acceptable. If the new meter was more accurate, how would you know? All companies test their products extensively. The FDA regulates clinical trials done by a medical department of companies. When these trials are done properly, they provide excellent data on which to base decisions regarding accuracy.
You need, however, to be sure the trials are unbiased, independent, and representative. Some characteristics of trials done properly are listed in Table 3. The testing site should be independent of the manufacturer. Ideally, it should be an academic or well-established clinical testing site. The study should have at least data points per testing segment individual meter or strip type and, to ensure accuracy in use, should be performed by people with diabetes.
Patients should do the testing themselves using a capillary blood sample. Ideally, the reference value should also be a capillary method, such as a YSI Yellow Spring Instruments, Yellow Springs, OH , but if the patients are truly fasting 4 h or more , a venous sample sent to the clinical laboratory and tested or at least centrifuged within 30 min is acceptable. And a crucial one.
Catching those times and intervening appropriately can, in theory, lessen the negative effects of the disease, which can include heart disease, blindness, limb amputation, and kidney failure. Their system consists of an ink made of glucose-responsive carbon nanotubes. The ink would be injected under the skin in a design a few centimeters square, creating a sugar-sensitive tattoo.
Updated June Know your blood sugar numbers: Use them to manage your diabetes. Updated March MIT School of Engineering. How do glucometers work? Published October 18, Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth.
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