Recently I wrote a post asking, "Why Can't Meters Tell Me My Blood Sugar?" It was prompted by checking my blood sugar on two different meters from two different companies, and to my surprise discovering the results were quite dissimilar.
I then did a home trial several times and each time saw different numbers pop up on different meters. I set off to find out why. I discovered why. I also discovered why meter accuracy is both more, and less, critical than we think.
Four different meters ranged from 121 mg/dl (6.7 mmol/l) to 158 mg/dl (8.7 mmol/l) in one test taken at the same time. (Ignore dates on meters, I rarely use the date function.)
Compared to a Standard Lab Test
Home meters can't compare to the standard lab test ("reference standard") they're measured against. Hospitals are contained environments where elements like temperature, humidity and altitude are controlled. Trained technicians run the test on a very costly machine that is regularly maintained and calibrated several times a day. Lab tests also analyze a larger blood sample for 60 seconds or more.
Home meters have to rely mostly on their test strips for accuracy. Strips are easily affected by variation in manufacturing, temperature, climate, altitude and freshness (age). Also, substances in our blood like medication (something as simple as Tylenol), and/or our own red blood cells can interfere with our glucose reading.
As for why different meters give different results, it's largely due to the meter's calibration and coding and the strips' design that causes a unique interplay between strip and meter.
The last wild card in our glucose reading is us, the user. Do you handle the strips properly? For instance, not use the one that just ricocheted off the honey-glazed chicken? Did you wash your hands so the apple you ate an hour ago isn't picked up by the strip? Are you using strips that expired last year?
So now you know why your home meter is not as precise as the reference standard. But that's only part of the story.
The Waterfall Effect
There is something else at play and it's this. Your blood sugar reading is only one of several factors from which we make decisions to keep our blood sugar in range. For the estimated 7.2 million people in the U.S. who have diabetes and use insulin, not to mention the tens of millions around the world, Dr. Barry Ginsberg, of Diabetes Technology Consultants, says meter accuracy plays only a small role in the overall accuracy of insulin dosing. Carbohydrate counting and insulin absorption are the main contributors to accurate dosing, and there are enormous errors in both.
Dr. Ginsberg told me the average error is only 8 percent if a meter meets the ISO standard (95 percent of the time it's within plus or minus 20 percent of a standard lab test at glucose concentrations equal to or above 75 mg/dl, and within 15 mg/dl at values less than 75 mg/dl).
Comparatively, the average error in carb counting is about 20 percent and in insulin absorption about 25 percent. Hence, a lot of inaccuracy to base my dosing on. Yet, notice meter accuracy is much less impactful to my dosing accuracy.
The solution, for now, is to make each of these three factors more accurate. So if we increase meter accuracy to within plus/minus 15 percent -- the new reference standard now pending FDA approval -- and I brush up on my carbohydrate counting and get a little better at calculating my insulin dose, I'll increase my chances of getting my insulin dose more accurate more of the time.
So, do I want my meter to be more accurate? Absolutely. Dr. Ginsberg says at the current standard people with Type 1 diabetes are missing 15 percent of hypoglycemic events (low blood sugar below 70 mg/dl (3.8 mmol/l). Within 15 percent accuracy we'll still miss 10 percent of hypos. We need to get meters to within 10 percent accuracy to miss no more than 1 percent of hypoglycemic events.
Meters are moving toward greater accuracy. Some are already satisfying the new proposed guideline of plus/minus 15 percent, like the OneTouch Verio IQ and Pro, and the recently-released Nano from Roche and Bayer's Contour next EZ. There are likely more; these are the ones I know. Also, industry insiders say Agamatrix meters and strips, packaged under Medicare's Liberty Medical, Kroger and Target brands, and Sanofi's new iBGStar, are closer to within 10 percent of a standard lab test.
But I'm not just concerned about catching hypos. I want to be able to keep my blood sugar in my target range as much as possible to avoid long-term complications.
So in addition to improving meters' accuracy, I want the food industry to tighten their accuracy on nutrition labels. I want dietitians to explain how foods impact our blood sugar, like how fat in a meal slows down blood sugar's rise. I want health care providers to provide better instruction on using insulin, like where on your body you inject affects the amount, and rate of, insulin absorption, and that being sick or stressed usually raises blood sugar.
And I want those who blame patients for not having the blood sugar numbers you think are simple arithmetic to realize that they're not.
In the meantime there are a few things we patients can do to increase our dosing accuracy: wash our hands, brush up on our carbohydrate counting, learn more about insulin dosing and choose our meters wisely.
Note: I want to thank those who generously shared their time and information with me: Dr. Barry Ginsberg, President, Diabetes Technology Consultants; Dr. Alan Cariski, VP, Worldwide Medical Affairs, and Medical Safety Officer at LifeScan; Dr. Holly Schachner, Pediatric Endocrinologist and Medical Affairs Officer at Bayer Care; Dr. Andreas Stuhr, Medical Director North America at Roche Diagnostics; Dr. Sridhar Iyengar, Director and CTO at Agamatrix and Shawna Gvazdauskas, Vice President, Head of Devices, US Diabetes at Sanofi. I want also to express my respect and admiration for those who are working to improve meter accuracy.
This article was written on my own initiative, I was not asked to write it nor was I compensated by anyone or any company.
Riva speaks to patients and health care providers about flourishing with diabetes and is the author of "50 Diabetes Myths That Can Ruin Your Life and the 50 Diabetes Truths That Can Save It" and "The ABC's Of Loving Yourself With Diabetes." Her third book, "Diabetes Dos & How-Tos," will be available late September. Visit her website DiabetesStories.com.
For more by Riva Greenberg, click here.
For more on diabetes, click here.