There are several key characteristics of glucose meters which may differ from model to model:
- Glucometer Readings: Size: The average size is now approximately the size of the palm of the hand, though some are smaller or larger. They are battery-powered.
- Glucometer Readings: Test strips: A consumable element containing chemicals that react with glucose in the drop of blood is used for each measurement. For some models this element is a plastic test strip with a small spot impregnated with glucose oxidase and other components. Each strip is used once and then discarded. Instead of strips, some models use discs that may be used for several readings.
- Glucometer Readings: Coding: Since test strips may vary from batch to batch, some models require the user to enter in a code found on the vial of test strips or on a chip that comes with the test strip. By entering the coding or chip into the glucose meter, the meter will be calibrated to that batch of test strips. However, if this process is carried out incorrectly, the meter reading can be up to 4mmol/L inaccurate. The implications of an incorrectly coded meter can be serious for patients actively managing their diabetes. For miscoded meters, the probability of making an insulin dose error of 2 units is 50%. The probability of making an insulin dose error of 3 units is 24%, compared to 0.49% when using a no coding meter. This may place patients at increased risk of hypoglycaemia.
- Glucometer Readings: Glucose vs. plasma glucose: Glucose levels in plasma (one of the components of blood) are generally 10%–15% higher than glucose measurements in whole blood (and even more after eating). This is important because home blood glucose meters measure the glucose in whole blood while most lab tests measure the glucose in plasma. Currently, there are many meters on the market that give results as “plasma equivalent,” even though they are measuring whole blood glucose. The plasma equivalent is calculated from the whole blood glucose reading using an equation built into the glucose meter. This allows patients to easily compare their glucose measurements in a lab test and at home. It is important for patients and their health care providers to know whether the meter gives its results as “whole blood equivalent” or “plasma equivalent.”
- Glucometer Readings: Data transfer: Many meters now have more sophisticated data handling capabilities. Many can be downloaded by a cable or infrared to a computer that has diabetes management software to display the test results. Some meters allow entry of additional data throughout the day, such as insulin dose, amounts of carbohydrates eaten, or exercise. A number of meters have been combined with other devices, such as insulin injection devices, PDAs, and even Game Boys. A radio link to an insulin pump allows automatic transfer of glucose readings to a calculator that assists the wearer in deciding on an appropriate insulin dose. One model also measures beta-hydroxybutyrate in the blood to detect ketoacidosis (ketosis).
- Volume of blood sample: The size of the drop of blood needed by different models varies from 0.3 to 10 μl. (Older models required larger blood samples, usually defined as a “hanging drop” from the fingertip.) Smaller volume requirements reduce the frequency of unproductive pricks.
- Glucometer Readings: Alternative site testing: Smaller drop volumes have enabled “alternate site testing” — pricking the forearms or other less sensitive areas instead of the fingertips. Although less uncomfortable, readings obtained from forearm blood lag behind fingertip blood in reflecting rapidly changing glucose levels in the rest of the body.
- Testing times: The times it takes to read a test strip may range from 3 to 60 seconds for different models.
- Display: The glucose value in mg/dl or mmol/l is displayed in a small window. The preferred measurement unit varies by country: mg/dl are preferred in the U.S., mmol/l in Canada and Europe. (To convert mmol/l of glucose to mg/dl, multiply by 18. To convert mg/dl of glucose to mmol/l, divide by 18 or multiply by 0.055.) Many machines can toggle between both types of measurements; there have been a couple of published instances in which someone with diabetes has been misled into the wrong action by assuming that a reading in mmol/l was really a very low reading in mg/dl, or the converse.
- Clock/memory: All meters now include a clock that is set for date and time, and a memory for past test results. The memory is an important aspect of diabetes care, as it enables the person with diabetes to keep a record of management and look for trends and patterns in blood glucose levels over days. Most memory chips can display an average of recent glucose meter readings.
Hospital glucometers: Special glucose meters for multi-patient hospital use are now used. These provide more elaborate quality control records. Their data handling capabilities are designed to transfer glucose results into electronic medical records and the laboratory computer systems for billing purposes.