The problem with blood glucose meters, which everyone who has diabetes relies on, is that they are sophisticated devices, which makes them more prone to user error and potentially to other problems. These devices are so common now that we take them for granted and can often get one free. But they were initially intended for hospital use, and it wasn’t until 1970 that the first person with diabetes got one.
Accuracy and inaccuracy
Accuracy refers to the closeness of a measured value to the true value. Blood glucose meters can’t be perfectly accurate, where every test result is correct, but they are slowly getting better. The U.S. Food and Drug Administration (FDA) determines the proportion of the meter’s blood glucose results that have to be correct at different blood glucose levels. Here are the current standards.
Precision and imprecision
Precision is independent of accuracy. When your meter results are consistent — for example, if you test twice and get the same result both times, but the results aren’t close to the true value — you have precision but not accuracy. If your meter tests either too high or too low, it is imprecise. If it’s not too far off, this may be less of a concern than inaccuracy, which can have serious consequences.
Sources of inaccuracy
Meters return inaccurate results because of four general reasons:
Using damaged or outdated test strips is probably the biggest strip problem. Discard those that are outdated, exposed to heat or humidity, or are near the expiration date. Also discard any that have been damaged, in a damaged container, or one that has been left open. If you still use a meter that must be coded to each container of test strips, be sure the meter’s code matches the test strip container.
Temperature, humidity, and altitude can make blood glucose readings inaccurate. But all of the leading meters from the four companies with the largest market share (Roche, LifeScan, Abbott, and Ascensia) now have such wide ranges than only extremely high and low temperatures or humidity affect the results. And all of them have been tested up to 10,000 feet.
New meters from the leading manufacturers don’t interact with “the most dangerous substance,” icodextrin, used in some peritoneal dialysis fluids. But a D-xylose absorption test can affect any of them. High tolazamide, uric acid, or pralidoxime can affect LifeScan meters. High triglycerides, galactose, or ascorbic acid can affect Roche meters. High triglyceride or cholesterol can affect Ascensia meters.
The cause of incorrect meter readings is often a mistake by the person who is doing the testing rather than by the device itself. Blood glucose meters are one of few blood testing devices that the FDA lets untrained people use. In a complementary slideshow here, I identified the 10 worst mistakes that people with diabetes commonly make when checking their blood.
Time for a new meter?
Now that you are thinking about your blood glucose meter, this would be a good time to study its specs. Check the owner’s manual and FDA.gov for its “510(k)” approval. But consider replacing it, if it’s more than a year old. You may be able to get a new one at no cost. A meter that you have used for awhile can have invisible damage. And one of the latest meters might have an improvement you would like.