A little information on checking how good your BG meter is in terms of accuracy and precision.
First, here is a quick explanation of the difference between “precise” and “accurate”:
precise-or-accurate
If you are wondering how good your meter is, there are a number of sites that give ratings. So you can start with checking your meter against these sites:
diatribe - blood-glucose–18-meters
Diabetes Technology Society Blood Glucose Monitor System
integrateddiabetes-blood-glucose-meter-comparisons
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Most important (that’s why it’s listed as #1 !), whenever you are checking your blood sugar, and whenever you want to validate how good your meter is, use proper technique - clean and dry fingers! If your fingers have food on them, particularly sweet foods, you can’t blame the meter…
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Try to check your meter when your blood sugar is not rapidly going up or down, and is in a somewhat normal range, like 80-120 mg/dL (4.4-6.7 mmol/L). Meters are not as accurate for blood sugar that is extremely high or low. (See Table 2: http://sites.bu.edu/bionicpancreas/files/2016/11/Comparative-Accuracy-Meters-Ekhlaspour-J-Diabetes-Sci-Technol-2016.pdf )
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When you are checking your own meter, a very easy and useful thing to do is do several tests at the same time, even using the same drop of blood if possible. When doing two tests back-to-back, if you see close numbers like 94 and 96 mg/dL, that’s not bad. If you see numbers a bit further apart like 94 and 117 mg/dL, that’s worse. The same drop of blood should always give you close results. If you are not seeing close results, it would be a good idea to start looking for a new meter.
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Keep in mind, meters are generally within a few percentage points of your BG value. So the higher your BG is, the bigger a difference that percentage will make. As an example, imagine your meter is always with 5% of the correct value:
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If your BG is 80 mg/dL, 5% of 80 is 4 points, so your meter would be between 76 and 84.
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If your BG is 300 mg/dL, 5% of 300 is 15 points, so your meter would be between 285 and 315.
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In the first case (when your BG is 80 mg/dL) you have a 8 point swing, from 76 to 84. But in the second case (when your BG is 300 mg/dL) you have a 30 point swing, from 285 and 315. In this example, that same 5% difference went from 8 points to 30 points.
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Occasionally you may see a crazy number. This can happen with any meter. If your meter throws out a number that seems wrong, wash and dry and re-check. The key word is “occasionally”. If it happens a lot, you should consider looking into getting a new meter.
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Using your CGM numbers to validate your meter won’t be useful for determining if your meter is accurate. It’s fun to see that your CGM matches your meter reading. You can be happy and excited about it, but it really isn’t a good test for meter accuracy.
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Using your A1C result to validate your meter is not extremely useful. The average BG to A1C scale is not exactly the same for everyone. Average BG and A1C do not line-up perfectly. So you can’t look at your A1C and BG average and say your meter is good or bad.
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Additionally, your meter average is not the same as your average BG. Your meter average is only the same as your average BG for the times you have tested. Generally more tests are done before and after meals, and before and after going to sleep. Also, people generally will be more likely to do repeated tests when they are high or low, and less likely to repeat a test when their BG is good. So average BG is not useful for validating meter accuracy.
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It is helpful validate your meter with a lab blood test. This is easy to do. When you are getting your lab tests done during your endocrinologist visit, right before they draw the blood you should check your BG with your meter twice. Write the numbers down! When you get your endocrinologist’s lab blood test results back, they will usually have the blood glucose value as part of the blood test panel they performed. Compare the lab BG value with the results you got from your meter right at the same time as the blood test (which is why you wrote those numbers down!). Those numbers should be close, particularly if you were in normal range.
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Even if you use your CGM much more than your BG meter, and think the CGM is more useful for you, keep in mind that you are using your BG meter to calibrate your CGM. So it is important to have a meter you can trust with good values.
Just a few points on checking how good your meter is. Please feel free to ask questions.
