As a CGM newbie I was thrown into the deep end to learn about Time-In-Range when it popped up on my Dexcom Clarity report.
Broadly (correct me if I’m wrong) the standard range for Time-In-Range is 70 to 180. That’s what my Clarity report defaulted to and it actually mostly makes sense to me too.
Here’s an interesting scattergram from a paper this year, showing Time-In-Range vs A1C for T1’s. I’m guessing it’s hard to have an A1C below 6, without having Time-In-Range at 60% or more likely 70-80% TIR.
But also note that one of the dots, the one in the extreme upper right, represents time in range better than 60%, but A1C over 12. I’m guessing more than half the time, that guy might be 150 or 170 (which counts as in-range), but the rest of the time he’s at 300 or 400.
Also note the cluster of most points in the scattergram, agreeing with what I’ve been reading in research articles, most T1’s today are 8% A1C and circa 40-50% time in range.
There is no such thing as a standard range. Dexcom defaults different people to different values and you can change yours to whatever you want in the Clarity settings. My settings are at the original defaults that Dexcom gave me which is 55-150 between 6AM and 10PM and 55-130 between 10PM and 6AM. When I am testing new foods, exercises, etc. my time in range is at 97%+ and when I am not doing any testing then 30 TIR is at 100% of these values. My last A1C was 5.6%. Standard deviation, of course, is also an important factor and I keep mine as close to 18 as possible. During food or exercise tests, it can go as high as 20 mg/dl
I’m not a fan of the study itself because they’ve defined hypoglycemia as below 70 and their conclusion is that people with low A1cs spend more time “hypoglycemic.” Since people without diabetes can dip into the high 60s fairly often, it really matters whether these “hypoglycemic events” are in the 50s or the 60s.
In reality, I believe that people with type 1 with a higher A1c can roller coaster more and are actually more likely to experience severe hypoglycemic events. I think this is supported by studies, but I’d have to look it up.
They only studied these people for 6 days and they used a Medtronic cgm during that time (not the best reputation…).
Given all of the above, the study doesn’t seem to be adding much value and could potentially contribute to uneducated doctors chastising people for having a low A1c because they think that means they must be having hypos. I’ve experienced this in the past, and it’s really annoying.
I’m OK with 70 being the lower end of time-in-range. Right around 70 is where I might start feeling hypo symptoms when I have good hypo sensitivity.
In part I started this thread because after 11 days on the G6, Clarity is telling me my Time-In-Range (70-180) is 95%. And that seems completely off the chart good in articles I’ve found about time in range where 30%-60% seems to be the usual ballpark for T1’s. At same time my A1C is better than 98% of T1’s so maybe I shouldn’t be surprised.
I have my time in range between 65-160 during the day and 65-180 at might. I make a higher allowance for the night because of my DP and I don’t want to wake up to deal with it more, since it can be variable and I can’t set my pump for variable only for the mostly minimum I need for it. I have stayed around 97% in range average and have quite a high percentage of 100% in range. My A1C is 6%.
Lol. one thing I’ve found is that if you are on this blog, you care more than most people! It doesn’t mean you necessarily have a lower A1C, because some people have harder issues to deal with, but it means you care more and probably are trying more than most.
And generally I think a lot of us are considered better controlled than “most”.
Where you are functioning right, is not based on a number, strictly speaking. I will not drive when I hit anything below 40 but in weeks that I am running at an average of 75. I feel perfectly fine and normal at 55. Where you function properly is a result of where you are and where your body is used to being. For someone that is used to running 200 normally, they will not function properly at 150. That is why both time in range and standard deviation are so important. If you run at 70 with a very low SD (Standard Deviation) of say 18 or less, then feeling just fine and functioning at 55 should feel perfectly normal.
I wonder if our perception of feeling fine when below 70 actually squares with an objective measurement of feeling fine. I have lived through many episodes of feeling OK when I’m surprised by a finger-stick < 50.
I suspect that if I were given a memory or other logical thinking test, I would likely fail when I’m low but not sensing that low – in other words, hypoglycemia unaware. I’m not too confident about a diabetic’s perception of being low is a dependable gage of actual cognitively-impaired hypoglycemia.
By the way, when I attended the TCOYD T1D retreat a few weeks ago, there were many references from speakers about the standard range for clinicians and researchers being 70-180 mg/dL. From a patient who values being measured against a customized range for my individual clinical setting, I prefer 65-140 mg/dL for my “standard.” Sixty-five mg/dL is the level that I’ve consistently and repeatedly start to experience adrenal-mediatied counter-regulatory action.
You could see if your reaction time changes significantly at different BG levels. Probably lots of online reaction time tests. Here is one. I have no idea how accurate or good it is. It was just at the top of a google search.
I personally try to keep my range between 70 and 150 but keep the clarity settings at 70-180 as I believe most articles, when they talk about time in range, refer to 70-180 as the standard as you suggested. At 70-180 my time in range is 98%-99%, my standard deviation is below 20 and me average BG is below 110. Everyone has a different target for all these measures and different actual results. There is no right and wrong. We are all different. I think the important thing is to continuously try to improve and when you reach your target change your target to a more aggressive target.
With AGP set to 70/150 my TIR is 73%, but if I switch it to 70/180 it is just shy of 90%. So the difference is in the number of data points between 150 and 180.
In drivers ed back in 1964 a contraption was set up in class to test our reaction time from foot on the gas pedal, to braking. All of us guys were so competitive we’d hit that thing so hard it was difficult to keep the whole thing in one place on the floor and it was a fairly large device. The next time I recall testing my reaction time was by my K/D ratio in Call of Duty, and I was in my 60’s. LOL!
I don’t think TIR is a very good indicator of overall control as a comparison against others (diabetics and non diabetics). You can move that number all over the map based on the range you choose. Unless everyone uses the same range its meaningless for that purpose. Even if the range is the same for everyone, IMHO a better indicator is average BGL and standard deviation. If I’m not mistaken, average BGL correlates reasonably well with A1c.
But it is a great tool for monitoring your own success against your own goals. If my TIR gets too high, I see that as an opportunity to narrow the range and raise the bar.
