Starting off with the Dexcom G5

[submarinerLV]

Hi Guys

Right ok, so let me begin by saying after tons of research into CGM's, I decided to plump for the Dexcom G5 & am currently on Day 9. I have a series of questions that I wanted to ask the experienced Dexcom pros out there as follows:

1) Cost, is a massive bug bear with the G5. On that basis, I've been using the original first sensor where I am currently on Day 9 & it's still giving great results / accuracy in comparison to the BG meter. That being said, I've heard various people saying they can push they sensors with great accuracy for up to 28 days in some cases! I love the sound of that, but how will I start seeing the G5 sensor failing? Will it be just through a total lack of accuracy where the readings are massively off or will I get an error message come up???

2) Even though I have the G5, I'm still doing as many, if not more finger tests on my BG meter. Is this normal or will this wear off? I think it's just more to the fact that I don't feel that full trust in the CGM technology because of the different measures fluid & delay.

3) Here in the uk, we are measuring glucose in MMOL's. Therefore, what is the accepted + & - tolerance on the G5? Some places I've heard it's 1.1 mmol's + or - & in other circles I've heard it's 20% + or - . What's the actual verdict please?

Overall I just want the G5 to work for me because I really can see the benefits with it. I just need to have my confidence in the system increased.

 

[tim2000s]

@submarinerLV - hopefully this will answer your questions.

1. What you'll see is that your calibrations become further away as the sensor starts to fail and what I see is that the data gets "noisy". By that I mean it jumps around a lot and instead of seeing a nice "line" you see it more as a "cloud with a trend to it". Eventually, it ends up with a ??? reading when it has fully failed. I've only occasionally got 28 days out of a sensor, but many people do achieve that.

2. I'd say that is not unusual very early on, but most people have got beyond finger prick testing to compare to the CGM after about a week.

3. I'm not sure I understand your question? Do you mean in reference to the blood tests? The Dexcom G5 is stated as having a MARD of 9%, which is taken in a lab setting. It also doesn't measure blood glucose, but glucose levels in interstitial fluid, so isn't necessarily going to match. Personally, I don't worry too much if it's 1 mmol/l or lower out at a blood reading of 6 mmol/l. That's why you have the ability to calibrate it.

I have one for you - what are your concerns with the system? What do you need to learn to gain more confidence in it?

I ask these things because I run a closed loop system using the Dexcom G5, where the "artificial pancreas" makes decisions based on the data that the G5 provides and I find it very effective for this. Most of the closed loop trials also use Dexcom G5 for their "Artificial Pancreases". Generally it is considered the best of the readily available CGM systems.

 

[submarinerLV]

Hi Tim

Thank you for the reply & for addressing all of my questions.

1) Ok, so with regards to calibrations, are we talking here the customary 2 calibrations per day, 12 hours apart? Does it matter a great deal if you don't always get these exactly on the 12 hour mark? Also, what's your usual wearing time you manage to get out of a sensor before you look to change it for a new one?

2) I want to have more confidence in the system & I'm sure that will come the longer I use it.

3) Apologies for the confusion but I'll break it down as follows. In one case I've heard that when measuring in mmol's like we do in the UK that's set up on a BG machine & the G5, if for example you do a BG test on the machine & its 6.0, then the Dexcom G5 is allowed to be within 1.1 mmol's of that result. So a maximum minus of 4.9 & a maximum plus of 7.1 Now, I've also heard that the Dexcom operates a 20% rule where it can be plus or minus 20% of a BG machine test so in this case if you were to do a BG test & its 10.00 then on the Dexcom it can be a maximum minus of 8.0 or a maximum plus of 12.00. Which is the actual correct answer??

Ok, so onto my concerns & this bears fruit to what happened to me recently. Just over a month ago I suffered a heart attack (just turned 35!) & when I was in hospital I met with one of the cardiologists who was wearing the Dexcom G5. It was from that moment on that I decided that I wanted to find out more about the system. I was given a trial of the Freestyle Libre & it was ok, but just ok. I wanted more control from seeing continuous updates results just like a CGM & I wanted to get the most accurate CGM on the market, to which I believe the G5 is that current model? On the flip side of this, if I was to pay for the transmitters & replace the sensors every 7 days, the costs would be astronomical for me, so while I don't want to take the mick, I also want to get as long as I can out of a sensor at any given time so that it's still giving me accurate results but not breaking the bank at the same time.

Thanks for all of your help Tim.

 

[tim2000s]

Hi Tim

Thank you for the reply & for addressing all of my questions.

1) Ok, so with regards to calibrations, are we talking here the customary 2 calibrations per day, 12 hours apart? Does it matter a great deal if you don't always get these exactly on the 12 hour mark? Also, what's your usual wearing time you manage to get out of a sensor before you look to change it for a new one?

On the calibrations, I generally calibrate less frequently than that. Usually once a day at beast in the first 10-12 days, as it has consistently proven to retain a good level. Once I get beyond that, twice a day becomes required, and after about 25 days, I found I needed to calibrate three times per day to maintain consistent readings.

I typically change mine between 14 and 21 days, as that's when my data starts to get messy , which isn't all that useful when you're running an artificial pancreas off it. That's just me though. There are plenty of people who change them at 28, 35 and 40 odd days. It's really dependent on when you see the data going bad, and each person seems to be different.

3) Apologies for the confusion but I'll break it down as follows. In one case I've heard that when measuring in mmol's like we do in the UK that's set up on a BG machine & the G5, if for example you do a BG test on the machine & its 6.0, then the Dexcom G5 is allowed to be within 1.1 mmol's of that result. So a maximum minus of 4.9 & a maximum plus of 7.1 Now, I've also heard that the Dexcom operates a 20% rule where it can be plus or minus 20% of a BG machine test so in this case if you were to do a BG test & its 10.00 then on the Dexcom it can be a maximum minus of 8.0 or a maximum plus of 12.00. Which is the actual correct answer??

My only question is where did you hear that from? I've never heard it before (and honestly, it's not something I'd ever looked at). Dexcom state that they have a MARD of 9% which means an average of 9% from blood readings in a lab environment. As I mentioned, I tend to work off the basis that as long as it's within 1 mmol/l in a normal range (4-10mmol/l) then I'm happy with that. At more than 10 mmol/l all CGMs tend to have more widely varying results.

If you want a correct answer on this one, phone Dexcom technical support. They will tell you the answer as it will be what drives whether they replace a sensor.

Ok, so onto my concerns & this bears fruit to what happened to me recently. Just over a month ago I suffered a heart attack (just turned 35!) & when I was in hospital I met with one of the cardiologists who was wearing the Dexcom G5. It was from that moment on that I decided that I wanted to find out more about the system. I was given a trial of the Freestyle Libre & it was ok, but just ok. I wanted more control from seeing continuous updates results just like a CGM & I wanted to get the most accurate CGM on the market, to which I believe the G5 is that current model? On the flip side of this, if I was to pay for the transmitters & replace the sensors every 7 days, the costs would be astronomical for me, so while I don't want to take the mick, I also want to get as long as I can out of a sensor at any given time so that it's still giving me accurate results but not breaking the bank at the same time.

Thanks for all of your help Tim.

Your latter statement is true of just about everyone who is using the system in the UK. It's just not available on the NHS easily. I'd suggest you go and have a look at this which breaks out cost comparisons. For most in the UK, changing every 7 days just isn't an option, so most of us change sensors a lot less frequently, and I personally use the xDrip app on Android rather than the official app as it enables you to run the transmitter beyond the Dexcom imposed cut off period (up to 5 months instead of 3). There is also a well known cottage industry replacing the batteries of G5 transmitters meaning that you don't need to always buy a new one. I know of people that have gone for more than a year on the same G5 transmitter.

 

[DunePlodder]

@submarinerLV Don't get too tied up with the accuracy or otherwise. It's important to note that the official MARD precision figures are, as Tim says, compared to a Laboratory standard device, not the commercial meters you & I use. Those are, at best, +/-15%. So a "true" BG of 6 might read anything between 5.1 & 6.9.
I stuck with a G4 because the transmitters are less costly - they last up to a year. The actual sensors are identical.

Although I check the CGM readings several times a day, I may not actually calibrate for several days if the readings are good. The timing of calibrations is unimportant, but try to make sure your readings are nice & level when you do calibrate.

I'm on day 23 of my current sensor & it's still going well. I was averaging about 18 days but this box has been especially good between 3 & 4 weeks. You'll know when it's dying - the graph readings take on a "splattered" look. Occasionally though it will recover & continue for a day or two more.

 

[submarinerLV]

Thanks all for the reply. Just as a quick snapshot, I'm currently on Day 10 of the sensor. Here's a screenshot. Still running well? I take it if the sensor was failing at this point then the graph would be all over the place?

 

[DunePlodder]

The sensor looks fine, & you must be pretty happy with the readings too!

 

[submarinerLV]

The sensor looks fine, & you must be pretty happy with the readings too!

Absolutely! I will just keep this current sensor in until it starts to look wayward. I keep to a really low carb diet & notice the results are even when not eating (no real bolus on board) , but I notice things start to change more when eating, like a bigger difference in the results on the G5 vs the BG machine. I suppose this is to be expected?

Also, does having a shower / getting the sensor / transmitter wet affect results?

Thanks

 

[tim2000s]

It would look more like this if it was failing.

 

[DunePlodder]

Yes, at higher levels differences may well be bigger, especially if your bg is falling or rising at the time.

I find that I sometimes get odd readings during/after a shower. This is worse with some sensors than others presumably because the transmitter doesn't always form a good seal with the sensor. If the problem is bad it is possible, with care, to remove the transmitter, dry it & re insert it.

 

[submarinerLV]

It would look more like this if it was failing.
View attachment 23041

Wow, thanks for posting that up! Can clearly see where there's a big difference. How long have you been using Dexcom for?

Also, there was mention about getting the batteries replaced in the transmitters. How & with who please?

 

[tim2000s]

Also, there was mention about getting the batteries replaced in the transmitters. How & with who please?

If you join the facebook group for "Dexcom G5 UK" and "xDrip G5" you'll be able to find some people.