Dexcom Users Direction Arrows

i am very curious if any other dex users have this problem w/ the direction arrows on the icon part of their receiver screen. even when my arrow it pointing straight, i can still be trending up or down. as well, i can sometimes get a direction arrow pointing down/up and not fluctuate at all. and sometimes i will get the double arrow pointing up/down (fast drop or rise) and w/in ten minutes the arrow goes back to being straight.

how much do you rely on these arrows to tell if your BG is dropping/rising/ or steady? i try and keep an eye out for the actual BG # on the screen, but i was wondering if this is best.
what do you do?

I actually rely on them a lot. Almost always when they are pointing down my bs is dropping rapidly and vice versa. As a matter of fact, when I get close to 130 with an up arrow I typically treat with 4u Afrezza which quickly controls the spike.

I do not rely on the “even” arrow for the reasons you state. I think the BG has to reach a certain “speed” before the arrow changes to up or down. A gradual incline or decline may not affect it. A guess.
The straight down arrow means that my BG will drop a number of points (maybe 30 or 40) then revert to level. The double arrow down is of more concern to me.

i get a total anxiety attack when those double downward arrows pop up and my BGs are already “in range” while that happens.

The arrows can sometimes mislead. Dr. Stephen Ponder (and T1D) in his Sugar Surfing book advises to follow the dots, not the arrows. Since he’s called my attention to this phenomena, I’ve noticed it more. Just the other day I watched a diagonal up arrow and a 109 reading transition to a diagonal up arrow and a 106 reading. In the next five minutes the system caught up with reality and then showed a sideways arrow and a 105 reading.

Overall, I find the arrows dependable but they sometimes lag reality. The dots usually tell the more accurate story sooner than the arrows. And I always double-check the double up or down arrows with my meter since that situation, if true, can call for a sharp response of a significant insulin correction or some fast acting glucose.

The Dexcom G4 User’s Guide advises:

Do not overreact to the rate of change arrows. Consider recent insulin dosing, activity, food intake, your overall trend graph [the dots!] and your blood glucose value before taking action.

Additionally the User’s Guide reminds us that the flat arrow does not always mean no change. A flat arrow means that the glucose value is not changing by more than 1 mg/dl per minute. It could change by up to 15 mg/dl in 15 minutes and still show a sideways arrow.


guess I’ve just come to rely too much on my Dex. :grin:

1 Like

To follow up on what @Terry4 nicely explained, here is an example that illustrates how the Dexcom arrow can be somewhat misleading. Arrows are useful, but following the dots is even better. As another alternative, which I find super convenient and useful, shown is a Pebble watchface developed in the Nightscout project.


Out of curiosity, has your opinion about CGM changed between now versus before you started using CGM?

Hey John,

Honestly didn’t have much of an opinion of CGM before I started using my Dexcom.

I can tell you that I cannot live without it now. It is such a powerful tool in my diabetes treatment. I understand CGM is not for everyone, but for me if I don’t have it, it’s like driving to a destination you haven’t previously visited without directions.

1 Like

yes. plain and simple. before having my cgm, my A1c was 8.9 and since being on the dexcom my latest A1c (taken this week) is 6.4

i have learned so much about myself, my D, how foods effect me BETWEEN the old multiple finger sticks. i have been able to make changes in my pumps profile which has helped enormously. i can be really frustrated w/ it often, b/c i have so much trouble finding good sites (as i have said MULTIPLE times, i am very lean and don’t really have the proper realistate to use for my sensor.) but all in all, i doubt i would give it up. i just keep on listening and reading suggestions on TuD and everyone has helped me along.

I hope this doesn’t come across wrong, but … if you were apathetic to CGM then one would expect you never would have started using it. So, you must have had at least some slightly positive view of it, yes? No? Maybe?

Why did you bother to start using CGM if you had no interest in it? :confused:

Something my endo brought up to me at an appointment. He knows I like to try things to treat my diabetes and he suggested it so I went for it. Honestly, I was testing 15-20x a day and was ok with it so I never really researched CGM. Glad my Endo brought it up. :smile:

Hey Terry-
One of my favorite topics, right?
Anyway I do love the arrows. My reason being before I felt like I was pumping blindly. It’s one thing to get 150 on a meter. It’s another to get 150 with 2 arrows going up. I would probably bolus and watch to prevent that high from creepy up. That same 150 with 2 arrows down would call for another course of action. I probably wouldn’t bolus for a slightly higher number and watch and see how quickly it’s dropping. I do love those arrows. I think they give me a much better idea of when to correct or not.

1 Like

@Sally7, I know we’ve exchanged views on this topic recently. I can appreciate going from fingerstick and little trend info to a CGM and their helpful arrows. That is a plus. I hope you can now appreciate the point I was trying to make that while the arrows help, sometimes you need to zoom in a little closer to the data frontier and look at the change between the last few dots. Especially when the dots and the arrows disagree. :wink:

To put it another way, you want to be aware not only of what the rate of change of your glucose is (first derivative), but also of how quickly and in what direction the rate of change is changing (second derivative).

(Sheesh. To think some people still ask what possible use in their day to day lives calculus will ever be to them. :confounded: )

1 Like

Or to put it a third way. It’s how fast you’re going and how fast you’re changing how fast. If we haven’t lost math avoiders yet, we’ve surely done it now! :open_mouth:

(I only took one class in calculus and I was surprised to learn it was in in-depth study of slope!)

1 Like

Exactly! I have to say I’ve had hard time resisting the urge to bring up calculus to this forum. At the moment, bg is in target, first derivative = 0, second derivative = 0, life is good :wink:

1 Like