Factors Influencing Accuracy Of Insulin Dosing

Here is a great article by Riva Greenberg. Riva is a type 1 diabetic, and she writes articles for the Huffington Post. Her article concerns glucose meter accuracy, and other factors that influence our glucose control. The meter accuracy is important but accuracy in carb counting, and the levels of absorption of the insulin are also very important. Here is a quote from the article: "...... 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 approva -- 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."
In my case the insulin absorption is a major factor. After almost 62 years of injections, and 5 years of pumping, my body is riddled with spots of scar tissue. The level of absorption is very variable because of the scar tissue. I have to change programming on my pump every time I change infusion sets. When I change sets every 3 days I never know whether my absorption will be great, mediocre or poor. It was the same with injections. Some of my scar tissue is permanent. Be sure to rotate sites to avoid scar tissue. Here is Riva's article:


From one of the links in the article:

Finally, patients with type 1 diabetes need the greatest accuracy.6,7 They use glucose monitoring routinely to make therapeutic decisions and to inform themselves about hypoglycemia. In addition, these devices are now used to calibrate continuous glucose monitors and need to be very accurate. Although routinely used to make insulin decisions at meals, glucose monitors account for only a small portion of the total error in the absorbed insulin dose. Errors in carbohydrate counting are routinely 15–25%, errors in the constants used (carbohydrate-to-insulin ratio and insulin sensitivity factor) are routinely 10–25%, and insulin absorption from the injection site varies by 20–30%. Assuming these errors are independent, the sum of these errors is 27–46%. An error in glucose monitoring of 6% adds only about 0.5%, and doubling the error to 12% adds only 1.5–2.5% to that range.

The sum of these errors is 27 to 46%! Wow, this makes me wonder how I don’t hit 35 and 350 everyday! Could errors from I:C ratios, ISF, absorption, carb counting and meters really be that big??

It is scary, however hard we try it still isn't the same as having a working pancreas. This is partly why I am so wary of all the hype about the artificial pancreas, it will still be based on all these inaccurate calculations. But that's a another topic.

I don't see how carb counting can be improved, I weigh everything but then depend an a carb factor to calculate the amount of carbs, how accurate are these factors. I've seem different values, quite large % differences, for the same thing in different books. Think of something like fruit, an apple say, how does the type of apple or ripeness affect the carb content? But I still keep on weighing & calculating & basing my dose on the result. And if you don't use a pump the dose has to be rounded to the nearest unit or 1/2 unit. As Capin said it is amazing we don't hit 35 & 350 every day.

I think the numbers are true but I don't think everyone is a poor carb counter or has a bad I:C , we spend years fine tuning or insulin regiment and meals but I have never had much trust in the new meters.I recently had major surgery and suffered a massive amount of blood loss. My RBC is low and my Hematocrit is 28%, 40% is normal. After they discharged me from the hospital I felt like my BG was low all the time but my LifeScan meter said everything is good. After 5 weeks of feeling hypo I tried a diffrent meter and found out that the LifeScan product is sensitive to Hematocrit values and will overstate BG if Hematocrit levels are low.

Here are a couple of photos showing just how far the LifeScan meter was off...the Bayer meter tests the same or very close to my lab BG tests.![|373x480](upload://2ksscKpkhbOcWyQzkQal6lqEJTU.jpeg)

I think carb counting may also refer to the actual nutritional information. Nutritional information is only required to be so accurate. Does anyone know the accuracy requirements for the nutritional infomation on packaging?

Wow John what a tough headache! But hey at least you may have quite an enviable A1C.

How can a +-20% meter error become a +-8% ?
I know of scientific articles which found off the shelf well known meters no more iso compliant, as if manifacturing standards were way lower than quality used for ISO certification ....

As for absorbtion, it's for MDI not micro pumps.

They can round off the carb count and if it's less than one they can say zero. The total carb count on the nutritional information panel is accurate but many products have confusing serving sizes and if your not using a scale you can easily make a 20% mistake. Try to guess a serving when the package says 2.5 servings.

I think the FDA requires meters to be within +/-20%, but in acutallity most meters have accuracy of +/-8%.

Many diabetics do not use a book like the Calorie King to determine the carb count before bolusing. Some do not choose restaurants with nutritional info, and many do not have scales to weigh their food. Thus, the carb count must be done by guessing. That could contribute a major error in insulin dosing. It happens to me every year when we visit my son in Atlanta. I never know the carbs in my meals there, and I tend to underestimate and have highs while I am there.

Using a scale at home has some positive benefits for restaurant meals because we learn over time what a serving of carbs or protein looks like. I also learned food exchanges before carb counting became the preferred method for calculating a bolus and this has also helped me when eating at strange restaurants.There are many variables that we have little control over but life is much better for a PWD today, we no longer have to sit at home or hide in the shadows. I except the tools we have today with a smile...life is really good compared to the old days .

Yes John things are much better. I started in 1945 without being able to test my blood, not knowing about scar tissue problems, not having a doctor who knew much about diabetes, and using insulin from cows and pigs. HA HA! It is a wonder that I survived and have no serious complications.

Look at this 2009 scientific article (link).
They tested 27 glucometers and

More than 40% of the evaluated BG monitoring systems did not fulfill the minimum accuracy requirements of DIN EN ISO 15197:2003.

So 11 out of 27 "lost" ISO compliance when reaching the market ....

hope youre feeling better!

During the day, I'm much more consistent. I usually eat the same sort of things pretty regularly, although I've been splurging a bit lately, w/ some longer runs on my calendar, and not worrying about my weight as much. I tend to eat more at dinner, overbolus and then chill and drink beer and eat junk food to stave off the lows in the evening. Or keep dinner rolling along or whatever? I have Calorie King and a scale but don't use them all the time, again, mostly lunch because that's a bit more scientific than dinner?

I don't worry about meter accuracy that much. It seems to be pretty much in line with my CGM and A1C so it's ok w/ me. My A1C runs a bit higher than my CGM average. I don't bother d/l the data from my meter so I'm not sure if the meter is more or less accurate than the CGM, I'd guess less but, b/c of the "trends" thing, I'd sort of suspect that they'd even out, maybe the meter would have a slightly higher std dev, since I keep an eye on things and catch lots of "issues" sort of while they are happening...

Meter is used to calibrate CGM. An error on calibration affect CGM accuracy.
Think this way: if the meter measures always 20% less, your "perfect" CGM would measure always 20% less.
The problem is errors are never always the same, that would be an easy to fix drift. Bad errors are random.


I just became aware of a new assessment of the accuracy of 43 glucose monitoring systems. This has really good information. In general the results are encouraging and discouraging. It appears that some meters clearly could meet stricter standards, but many meters are just pretty inaccurate and have some systemic problems.

I have an Aviva Expert Brian, from what the report states, these meters seem pretty ok. My One Touch Ultra is a lost cause altogether.

I have had a lot of issues with the novo nordisk pens giving less than accurate doses. I spent three weeks thinking I was going nuts, when really my pen was giving me less than half the dose I was entering. I switched to syringes to remedy this. When my pharmacist finally convinced me to trust pens again, it happened a second time with a different pen!!!