Which would you change....Dexcom G5 runs 40 points low


It did pretty well yesterday so I was optimistic. Today is another story. This science project is not my first choice for a hobby. :slight_smile:


Alright…I’ve yanked the sensor. I’ve replaced the transmitter. Starting over. I’d rather have no data than bad data.

My transmitter had three weeks left on it, but it was manufactured on 2.5.18. I’d read by @Michael somewhere that past 12 months it could be screwy, I think, so hopefully a newer transmitter in another area of fresh skin will help.


If you have a lot of sensor batches, maybe try a recent one to see if there is a difference?


I already slapped one on from the last box that seemed to do okay. I’ll have to look closer at my batch options tomorrow for going forward.

My eyes feel so worn out from my bg swings today…or just highs…hard to tell the difference right now.


In case this helps anyone dealing with this themselves, it appears that the new transmitter (manufactured May 2018) is functioning much better, even just on Day 1, than my transmitter manufactured Feb 2018.

Every single fingerstick has been within 20% today, and usually closer than that. There has not been any noise today. I started this session last night, getting data starting around 9PM.

I’m using one of my oldest sensors and it is four months from expiring. I’ve been using that shipment for a while.


I consider the Dexcom transmitter to be only slightly more complex then a traditional meter. (Minor exaggeration perhaps but it is for the point.)

Just as I consider all the “magic” to be in the meter strip, I also consider all the “magic” to be in the Dexcom sensor.

IMHO the transmitter either works or does not work. There is no in-between. Strictly my opinion. Although I hold that opinion for every model of Dexcom Transmitter and sensor we have used.

BTW - When you pull a sensor that had horrible data, it might be worth to closely examine the sensor. The sensor should always be examined as standard practice to ensure the entire wire (ie - the fine tip of the sensor) is removed (for safety sake). However in terms of bad data, if the sensor looks very different from other removed sensors (and after examining them - you know exactly what it should look like) such as if it has dried blood on it then I assume it really was not Dexcom or the sensor but rather the location we used by random chance was simply not a good spot. Nicked a blood vessel or something.

Also - When changing the sensor out, are you careful to always wipe down the underside of the transmitter with an alcohol wipe? We are extremely careful to always do that to ensure we will have the cleanest contact possible. With the G4 and G5 transmitters (can’t remember on the Seven Plus) we would also periodically pop the transmitter out of a good sensor mid-session to wipe it down if the numbers started to seem wonky particularly if the wonky numbers coincided with a shower. We have never given any extra protection to any Dexcom transmitter/sensor in conjunction with water. But clearly with the non-G6 systems, there would sometimes get water between the transmitter and sensor which was easily resolved by popping the transmitter, wiping it down with alcohol wipe, letting it air dry then popping it back in.

The G6 physically does not allow the transmitter to be popped out in mid-session.


I’m in the habit of giving it a cursory check over after removal (generally look to see if it is bloody or bent), but I’ll start checking it more carefully.

I hear ya. I guess I’m unclear on what is defined as a “transmitter failure” under this thread:

Is a failure a transmitter that dies? Or is a failure a sustained performance failure wherein it will not stay within 20% of fingerstick?

I’ve been fortunate enough to get a bit of a cushion on G5 transmitters. But the thing is that when I get to activating one, it’s older than a freshly received one. I’ve noticed before decreased performance in the last month with some of my transmitters. And then when I start a new one, the issues seem to disappear for a while. Maybe I’m wrong on that, but I believe I have concluded this at least once before…whether or not I’m correct is another story. It’s hard to know what to conclude on a lot of these things. Stuff either works or it doesn’t…but tracking down the real cause is tricky.

Yup. Always.




I would call that a sensor failure.

BTW - The quote from @Michel that you had. Dexcom is not saying the transmitter goes bad after those dates. Or that the battery will stop. Or that any failure will happen. All Dexcom is saying is in order to have Dexcom replace a transmitter under warranty, the dates must be observed. Running outside those dates is running outside of the warranty. Which is entirely different from whether or not there are any issue or runtime or battery or anything. And even if running outside of warranty, you are still completely supported by Dexcom Technical Support. The only thing they (Dex Tech Support) is not required to do (when outside of warranty) is replace the transmitter at no additional charge.



But what I’ve been doing isn’t working. So I’m trying something else. I’ll keep watching to see what it does.

But for today, it seems to be helping.

And with diabetes, I’m taking it day by day.


@T1Allison, I cannot prove that a transmitter would not cause degraded readings—but I believe it is unlikely, although not impossible. My guess is that transmitter failure symptoms would be no signal, or a radical breakdown in the BG calculation that would be obvious. I think that @thomas is very likely right: degraded readings are much more likely to be due to the sensor, particularly an old sensor. I would always assume it is the sensor or the sensor batch, not the transmitter

But—I can’t totally rule out the transmitter as the cause. If you had repeated failures with several sensors, then are successful with all other sensors of the same batch using a new transmitter, we’d have to wonder if an old transmitter can cause degraded readings.

@Chris, what are your thoughts? Do you feel there is a scenario where a bad transmitter would cause degraded readings?


Well, I’m happy to keep testing it out bc I’m going to have to anyway. :grinning:


@Michel, I only ever started seeing this in the last year or so. I assumed it was along the lines of they want their product good enough that people buy it and use it…but not so good that it works flawlessly forever. Like how my grandma’s fridge lasted forever…and you’ll never be able to buy a fridge like that these days.

Could be totally wrong on all of that…but I’m de facto testing it out until it irritates me enough to ditch CGM altogether. Hopefully I find success before that point! :+1:


There is another thread where a possible change in the Dex sensor is discussed.

We definitely noticed a change around Summer of last year.

Which I feel is due to a manufacturing change with the sensor, nothing to do with the transmitter. I also do not think the change was intended to impact performance by Dexcom but rather they were making a change due to business relationship changes and/or trying to shave a little on the cost.

Whether or not what we noticed is the same as or related at all to what you are seeing - no idea.


You could give the Senseonics Eversense cgm a try.


I’ve never paid attention until now…but it looks like sensors only show expiration dates and not manufacture dates?

I’m currently using my sensors that expire 4/2019. I have another set that expire 9/2019…but the one I tried from that set is the one I just ripped out on Day 3 before changing the transmitter.

It seems to me that once the transmitters went from 6 month life to 3 month life (due to Bluetooth battery drain, I think) is when it seemed like quality degraded for me. Could be a false correlation. But I remember thinking this before.


IMHO most likely.

G4 Transmitters are six month warranty. (With fine print.)
G5/G6 Transmitters are three month warranty. (With fine print.)

My assumption is sensors get a 1 year expiration date stamped on them. (My guess based on when I order, the backlog, assumption on how long ago they were manufactured, when we get them and what the printed expiration shows.) But yeah - Dexcom sensor packaging is printed with lot number and expiration date. I don’t read much into sensor expiration date but @Chris would be a good one to ask as to the probability of a Dexcom sensor expiration date having much to do with reality assuming storage in ideal conditions.

I assume that anything with a 1 year expiration was decided upon by somebody with zero technical or scientific background.


Assuming/hoping this 4.2019 sensor stays reasonable for the duration, I’ll probably try one from my most recent shipment again and see how it does. So far, it’s still reading within 20% of fingerstick with no noise.


That is really good news.


Sure is! Thanks for the encouragement!


The most likely reason for one year expiration is that is how long they tested for. When making a product that is a disposable, you do some calculations about how many you will manufacture and how long it will take you to sell all of the sensors you have in inventory. Then you do testing to support your inventory system so that you will minimize the number of sensors you have to write off simply because they expired.

Normally, a product will roll out with a 3 month expiration and then over time the company will provide the FDA with the additional testing needed to support a longer expiration. This is simply because you have to age actual product for some of the tests and this takes a lot of time. Once you reach the point where your expiration assures minimal write offs, you stop because the testing is expensive.

The likelihood that the expiration has anything to do with the real world performance of the sensor is close to zero.