Diabetic Testing Inaccuracy Part 3


So in the end, you get the accuracy you need, but not much more. A lot of people will wonder about that. “Josh, if my meter is potentially 40+ points off between tests, how can that be accurate enough to administer my medicine?” Simple, you aren’t 40 points off. Your readings may be 40+ points different from each other, but they are(usually) no more than 20% from the actual result. That is why testing back to back is a problem. It creates a perception of a 40% error rate instead of a 20%. Plus, new diabetics are expecting the meter to be within as little as 2 points between tests. That’s not how any of this works. Results will vary wildly, but most of the time(95% of the time to be precise) they are within a 20% margin for error, which is a small enough error rate to validate any other findings based on that rate.
Let’s do an example. Say you are using insulin on a sliding scale. You need to increase the insulin dosage 10 units for every 50 points increment your blood glucose read over 150mg/dl.


Now let’s say that your blood glucose is actually 375. 20% of 375 is 75. Let’s say your meter reads on the outside edge of its potential inaccuracy and gives you a blood glucose of 450.

Instead of giving yourself 50 units, you give yourself 60 units of insulin. Oops, that’s too much….but wait, what if the margin for error was only 10%. That’s an increase of 37.5 points, giving you a reading of 415.5. Even with just a 10% margin for error, you would also give yourself 60 units instead of 50. Reducing the error rate to just 10 points per 100, would not create a single change in the amount of insulin you used on a sliding scale. There are a couple of reasons.

(Let me chime in here with a disclaimer, The Diabetic Shoppe does not, nor ever has made any recommendations concerning diabetic medication. Consult your doctor for that, and make no changes in your behavior concerning your diabetes based on this article) First, sliding scale insulin is usually an estimated dosage. Moving 1 single increment up or down the scale wouldn’t be devastating, or even counter-effective. Second, the effectiveness of the drug is directly correlated to the percentage of the error rate on the monitor. If your monitor is 20% off, then your drug distribution is no more than 20% off. In the above example, your blood glucose is 375. The insulin is going to bring it down.

In this blog, we don’t offer medical advice. Check with your doctor before adjusting any insulin dosage. The point of this section of the article is to get you to understand that SOME self-administered medicine just isn’t precise to the level that you may perceive it to be. When you take aspirin for a headache, you do not take 20% more or less aspirin based on your exact weight, current hydration levels, and the time of day it is. You probably usually take 2 or 3 aspirin. The amount you take, according to the bottle is very general. Enough that a rough estimation of your weight will give you roughly the correct amount to take. That is what a blood glucose test provides. It provides a rough estimation because a rough estimation is good enough. It ensures that the diabetic medicine you take is enough to help you but not enough to hurt you.


Imagine if aspirin was super precise. Imagine if you had to adjust the amount you ingested based on each and every pound you weighed. They would need a bigger bottle to fit all those directions.

Granted the more accurate the testing meter, the better you can directly treat your disease. That is why, at The Diabetic Shoppe, we only stock meters that we perceive to be very accurate. Also keep in mind that just because a testing meter can be 20% off doesn’t mean it usually is. In fact, the curve in our experience, is bell shaped. Very off readings are rare, and the farther from the mean you travel the rarer those results become. The most frequent results are also the most accurate. That’s why you shouldn’t freak out when your glucose meter reads 10 points higher than it did a few seconds ago. That proves the meter is accurate, not the other way around.


*The author of this blog is not a medical professional and this article does not contain professional medical advice. This blog is not intended to substitute for medical advice, treatment, or diagnosis. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of the contents of this article. If you think you may have a medical emergency, call 911 immediately.