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Are the current glucose meters accurate enough?

The FDA currently uses the standards set by the ISO for accuracy of blood glucose meters. These guidelines require meters to be accurate within 20% of the real glucose value, 95% of the time, when glucose is over 75 mg/dl and accurate within 15 mg/dl, 95% of the time, when blood glucose is below 75 mg/dl.

Below are the ISO guidelines outlining the accuracy currently required by the FDA for at-home blood glucose monitors:

Actual Blood Glucose Level Allowable Error
75 mg/dl or greater ±20% of actual reading (95% of the time)
Below 75 mg/dl ±15 mg/dl of actual reading (95% of the time)

Whether you feel current requirements are appropriate or not, there is no disagreement that most patients use blood glucose values to make critical decisions about insulin use and even to make choices about behavior (i.e., operating a vehicle). Under the current requirements, if your blood glucose is really 100 mg/dl, your meter could read anywhere between 80-120 mg/dl. This likely will not make a big difference in how you choose to manage your diet, activity, or medication use.

On the other hand, as the blood glucose rises, the meter reading could be more inaccurate, so for a blood glucose level of 160 mg/dl, the meter could display a number in the range of 128-192 mg/dl. Depending on what number is obtained in this range of possible glucose values, you would likely take different treatment actions (i.e., dose insulin at the higher end of the range and do nothing at the lower end). For blood glucose values below 75 mg/dl, meters are required to be accurate within ±15 mg/dl 95% of the time. This means for a blood sugar of 60 mg/dl, your meter could display a number in the range of 45-75 mg/dl.

You should keep in mind that these accuracy requirements only pertain to the “out of the box” error, so to speak – this is the error allowed under conditions in which the tests strips, meter, and the sample are handled exactly according to recommendations and under the assumption that no other influences are affecting accuracy. In reality, error could be higher than the ±20% or ±15 mg/dl, depending on a number of factors.

What factors influence accuracy?

Several factors can influence the accuracy of blood glucose strips and meters:

1. Patient Physiology: Meters may not be as accurate in patients with anemia (an abnormal level of red blood cells usually related to other illnesses) or sepsis (wide-spread inflammation associated with severe illness).

2. Environmental Interferences: Meters may be less accurate in high-altitude conditions, including on airplanes. In some cases the chemistry used may require a normal oxygen supply to work properly, being inaccurate at both low and high oxygen levels. Additionally, even other medications a patient is taking can affect the accuracy of a meter, as well as extreme temperatures and humidity. Most of these interferences are related to limitations of the chemistry used in the strips.

3. User-Generated Error: Several different user errors can also contribute to reduced accuracy of blood glucose monitors. In the next section, we discuss steps you can take to ensure you obtain the best results possible.

What can patients do to obtain the best test results?

You can help improve the quality of your blood glucose readings by following a few extra steps:

1. Wash, Rinse, and Dry Your Hands: Almost every patient cheats on this one, but it is one of the simplest things you can do to improve the quality of your testing. If you eat an orange or cookie for a snack in the morning and then test your blood sugar before lunch without washing your hands, your reading might be sky high, but completely false – you never know what you’ve gotten on your hands over the course of a day, so it is best to start with a clean slate before testing.

2. Keep Your Supplies Up To Date: Keep track of when your test strips expire. It is easy to convince yourself that they could still be good, but when you are using the readings to make decisions about your insulin doses, you want to make sure you are using fully functional strips! Along the same lines, you should be careful to store your strips in a safe place where they won’t be damaged—the glove box of your vehicle isn’t the best idea if you live in a hot area.

3. Perform Quality Control Tests: You may never have performed a quality control test on your meter or strips, but it is still a good idea to utilize this safety precaution built into the device. You can usually buy control solution at your local pharmacy, although it typically costs around $15 and expires in 30 days. We recognize this cost is high (and this fact was clearly discussed as a barrier with the FDA), but even if you can only perform control tests every now and then, it is better than never.

4. Read the Patient Information: Each manufacturer provides an insert in the box and/or on the box that lists information pertaining to the limitations of their blood glucose strips (i.e. temperature range, interfering medications, hematocrit levels).

5. When in Doubt, Check Again: If your meter reading seems inconsistent with how you are feeling, take the time to check your blood sugar again before dosing insulin. Remember, the standards are required to be met 95% of the time. You may have an “outlier” result that is outside of the 20%.
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