Dexcom trend arrows

Hello! I have been using the Dexcom G6 for about 6 months or so. It has been working well for the most part, but I have an observation/question about the trend arrows.

I have noticed a few times over these 6 months, and a few times with this most recent sensor, that the trend arrows are wonky (for lack of a better term).

For example, this morning, a couple hours after breakfast, my number was 122 with a diagonal arrow up. I thought to myself that I should keep an eye on that because I may need to give a correction bolus. However, as I was looking, the number updated to 115 with a steady arrow. I checked with my meter, and that said 118. It appears as if the number is accurate but the trend arrows are completely off.

Isn’t the trends the whole point of a cgm? Any thoughts? Thanks.

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A change of only 4 mg/dl in 5 minutes is considered steady. It’s a very small change. It doesn’t show a diagonal until the change is MORE than 5 mg/dl in those 5 minutes between readings.

At least it’s “steady” compared to the average diabetic that bounces around like a pinball.

That chart is a little weird, giving the values in different increments than the Dexcom works, you have to multiply the first numbers by 5.

Ignore that the chart is for G5 (which I just noticed. Sorry!), the trend arrows work the same with G6.

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Thanks, Robyn. That chart is helpful.

I guess I’m just confused by why my cgm said that I was 122 and increasing, but the next number was 115 and steady. So, it actually decreased from 122.

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But the arrow represents a trend over more than 5 minutes, per chart Robyn posted.

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My biggest learning curve when I first started using a CGM was to wait and see. That arrow will change direction quickly. And me being me who hates how I feel when I’m high would take a correction. Which than the next time I looked, it had leveled out and I would than be fighting the low.
So, I have learned to just watch and wait. Nothing in blood sugar happens super fast. You have time.
But I would say, your example happens all the time. One minute it’s heading up, than it levels out and sometimes heads down. I don’t normally check with a meter, as I have just let that one go. I just let the system do it’s thing. But I am in the class of people that wants easy and less work. So for me, the system has taken a lot of the “work” off my plate.
I wouldn’t worry about anything in your example. The numbers from CGM to meter are not that far off.
I use to worry because I am pretty sensitive to insulin as my correction factor is 1:100, and I worried that I would be crashing if the numbers were off, but I haven’t had any problems over the years with that happening.
So take a deep, breath, relax and just keep an eye on the CGM if you must but it sounds like it’s working fine.

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Wow, okay. I missed the bit where it says “in 30 minutes “ on that chart.

This is going to be a bit of a learning curve for me. I was given zero training when I got the Dexcom. I always assumed that if I saw 122 trending up, that the next number would be higher… even if only slightly. Apparently that is not the case!

So, what I’m getting from this is that I should not correction bolus based on trend arrows to head off a high blood sugar?

I take into account the last few values, trend, insulin on board, past/planned activity, before deciding to correct. All these things may impact bg and direction.

However, using Tandem pump, I wait longer to first see how it reacts.

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Except the trend arrows are based off of where you’ve been, not necessarily where you’re going. The trends change as it gets new info, but it only knows what’s already passed.

Predictions are different than trends. I know the G6 is capable of making predictions, but I don’t use any of the Dexcom software, so I’m not sure if you can see them. My Xdrip shows predictions, though, and my T:slim X2 bases it’s automation off of them. For the most part, though, you have to make an educated quess as to how to use the trend arrow, based on IOB, carbs on board, activity, etc…

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In my experience the trend arrow is based on delta in glucose over the past 20 or 30 minutes.

If I’ve gone down in the past 30 minutes, but up in the past 5, I usually get a down arrow, not an up arrow.

Sometimes if my blood sugar is zooming all over the place the Dexcom gives up and gives me no arrow !

Often half an hour or an hour after a meal it makes more sense to look at the second derivative. e.g. look for “top of the hump”. Does it look like it’s already maxed out and will soon be pointing downards? Or has it not begun to flatten off yet and is still going up and up?

Below is plagiarized from an article about G5. I’m not sure the G6 parameters are exactly the same but they seem very similar.

Here’s the full article: A Practical Approach to Using Trend Arrows on the Dexcom G5 CGM System to Manage Children and Adolescents With Diabetes

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Thanks to all of you for helping me to understand something I should have learned when I first started using a Dexcom! Now I will just need to re-learn how to use it. Also, thanks for the article, Tim.

This does explain why I sometimes get unexpected results after correcting for an anticipated high or low.

The deal with those arrows is confusing. They are not telling you if the current reading is rising or falling. It’s only comparing the last 3 readings to the current one.
It’s only useful to notice trends, but you can see that just by looking at the last 3 readings.

It doesn’t really mean anything in relation to the current number. You could level off or drop or rise at any moment.

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@Brianna1 – You’ve been given lots of good info already and I just want to make one additional point. If my CGM gets my attention and prompts me to consider adding insulin or carbs to head off an undesirable CGM trend, I always poke my finger to get a confirmation.

If the fingerstick differs from the CGM, I favor the fingerstick reading. If the fingerstick number is unexpected or differs too much from the CGM line, I’ll wash and dry my hands and poke again.

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@Timothy I am glad that I’m not the only one who finds the arrows somewhat confusing. As you said, you can see the trend by just looking at the graph for the last 3 numbers or so. Since the arrows are not telling you anything about what is going to happen, I’m struggling to see why they are there at all…?

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I use that too. Often the tandem pump arrow and xDrip prediction (red dotted line) show different directions.

I like sugarmate. It takes dexcom readings and will send to my watch.
It shows the value, the arrow and also the delta. So it will say

115 arrow and +10. That’s a useful think to have if I’m not looking at graph. I know I’m at 115 and that I was at 105, 5 min ago.

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The arrows aren’t predictions. The predictions are different colored dots in the graph. I don’t always have them, though. Haven’t figured that one out yet.

The different arrows are either missed communication between the two devices or because depending on your device, Xdrip can’t display a diagonal arrow in certain fields, like in your notification bar. One single Xdrip arrow up or down is the same as a diagonal arrow up or down on the pump or Dexcom display. Double Xdrip arrows up or down are equal to a straight up arrow on Dex/pump.

I just use the dexcom app but xdrip sounds like it could be better. Do you know if it’s only available for Android? I did a search on the apple App Store and didn’t see it.

I clarified my previous post.

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Correct, xDrip is android only.

There was an apple version called Spike, but not sure if still valid, and required non-app store loading.

@Brianna1 , @Robyn_H

Ladies, you all have hit the nail on the head. There is one little piece I have learned from my 20+ years on a Dexcom CGM (various models) and a pump, now a Tandem CIQ. The bits and pieces I have assembled with a little humor along the way. Here is my collection

CGM Calibration Facts & Rationale to Avoid Pitfalls

CGM Calibration Facts & rationale to avoid pitfalls & rabbit holes
NOTE: The term “rabbit hole” comes from the 1865 piece “Alice’s Adventures in Wonderland” by Lewis Carrol 1865 and has come to mean a bizarre, confusing, or nonsensical situation or environment, from which it is difficult to extricate oneself.

Test by finger stick (FS) anytime CGM doesn’t seem to match the way you feel.

Learn & verify acceptable deviation according to FDA approvals, ±20% above 100mg/dL and ±20mg/dL below 100. Examples, CGM =200, then FS can be between 160 & 240 and still be fine, or CGM = 70, then FS should be between 50 & 90 with level CGM.
C
Wait 60 minutes between tests if testing for CGM for validation.

Remember, CGM measurements are interstitial fluid and finger sticks are whole blood and glucose doesn’t move instantly.

Whole blood & interstitial fluid are physiologically different & 15-20 minutes apart in the movement of glucose.

Call tech support if 2 tests are >20% off, 1 hour apart. You may need a new sensor or have other technical issues.

Only enter calibration with great consideration. This reduces the number of times you will get into the calibrate, calibrate, calibrate rabbit hole. There are many who have avoided or not needed calibration for months after understanding the CGM actions.

If you are calling tech support for a goofy sensor, request replacement, regardless.

Follow tech support about changing a sensor.

Avoid the calibration rabbit hole of the system requesting multiple calibrations for hours and sometimes days.

Not everyone (some doctors) who prescribed insulin fully understands CIQ & how it uses CGM. See Section 3:CGM Features to learn more.

Why FSs & CGMs don’t play nice together.

First, FS & CGM are only expected to be within 20% of each other according to published standards accepted in the USA by the FDA. If your CGM says 200 then ±20% is ±40 mg/dL meaning a finger stick is fine if it is between 160 & 240. At the same time if CGM says 100 the ±20% would be 80 to 120. BELOW 80 it is ±20 points (mg/dL) without the percentage according to US FDA standards.

NOTE: Some individuals expect much narrower values between FS & CGM, even to the point of expecting them to match spot on, every time, all the time. This is unrealistic.

Second, as food is eaten, the food enters the blood stream in various places along the digestive tract. Some enters quickly from the mouth, like granular sugar placed under the tongue. Other foods swallowed quickly may not enter the blood stream until arriving in the stomach. The final absorption occurs in the small intestine.

After food is absorbed into the blood stream, it is ‘checked’ by the liver and then dispatched thru the body in the blood stream.

After glucose is in the blood stream, the glucose moves in the liquid part of the blood (sometimes referred to correctly as plasma or serum - like serum or plasma glucose for the doc’s office or hospital blood test) into the interstitial fluid that moves around all body cells outside the blood vessels. It is this interstitial fluid that CGM sensor wires are in to read the glucose and report it to our measuring devices.

The time for all of the glucose movement to take place is usually 15-30 minutes or more, depending on multiple variables including the amount of carbohydrates, proteins, & fats in the consumed food which changes the way the food is processed in the body.

It is this 15–30-minute interval and body fluid differences that give significant part to the variation in CGM and FS readings. This is also the reason most comparisons are done when glucose values are demonstrated level by the CGM before doing comparison finger sticks.

Wish they would play nice together……

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