My New Dexcom Plus

Hope you can help. Live in UK and just started Dexcom 7+ yesterday. I am type 1 using injections which maybe quite unusual as gather most people on Dexcom use pumps.

Three questions would be really grateful if anyone can help:

1. The calibration reminder vibrates every 12 hrs, how can i stop this from going off during night and thus waking me up?

2. How accurate is dexcom, i am in the `early need convincing` stage after so many yrs testing through blood, tested this mornng with two blood devices and was 3 points diff. Is it correct dexcom is more accurate the finger stabbing devices.

3. I find sensor looks quite big on skin, i know only cosmetic but is there any plans to reduce size or even blend better with skin colour.

Many Thanks


  1. Just calibrate before you go to sleep. The 12 hours is not fixed based on when you start the sensor or anything, it’s simply timed from the last calibration… you can calibrate “early” with no problem, and it resets the 12 hour timer. Occasionally if Dex gets confused it will ask you for one before 12 hours though (usually following any stretch of ???, or if you give it a calibration that doesn’t make sense based on where it “thinks” your BG is) If you ignore a calibration, nothing bad happens… it will keep on reading happily for a while. My experience is that if you ignore it too long, it will eventually go to ??? because it just isn’t sure what your BG is.

  2. You will rarely get “absolute” accuracy… much like testing between two meters, there’s some room for difference. Dex is most useful for seeing trends, not a minute by minute representation of your BG. You also have to keep in mind that what you see on the Dex screen lags about 15-20 minutes behind what a fingerstick will show. If your BG’s are usually fairly stable, the numbers may correlate very closely with your meter… but if they don’t, that’s not always a sign of a problem.

  3. I don’t find it that big… not compared to the MM version anyways. The transmitter used to be black which was much more obvious than the neutral grey they use now. I’d love to see a beige version come out… or to even just have beige tape.

Hi Sarah, Thanks for your quick response, really useful information, Chris

Sarah, Forgot to ask, first night gave me ??? symbol during night, am bit confused why this happens or if i can do anything to stop it, any thoughts?

Hey Chris,

I am another european using the Seven Plus and taking insulin shots. While it’s true that a lot of people on this forum seem to be using a pump, worry not as you’re not alone!

On the calibration issue, my receiver sometimes lights up at night asking for calibration, but it does not vibrate, and after a few seconds goes back to sleep. If this happens while I sleep, well… I keep on sleeping! :slight_smile: Not sure why yours vibrates, on mine I cannot see any specific setting that would modify the behaviour to silent mode.

Make sure you’ve calibrated your sensor properly, by choosing to install and calibrate during times of flat readings around the 120 mark, which happens to be the default figure when the receiver asks for the data input at the end of the 2 hours initial calibration window.

On the accuracy of the data, it is quite precise but do remember that blood-derived BG readings will always be quicker to be spotted compared to interstitial fluid BG readings. My experience is that the lag can be anywhere from 15 to 20 or even 25 minutes. The Dexcom box knows about the delay, of course, and tries to interpolate as much as possible. 3 points diff is sweet, and it’s way within tolerance for both the fingerstick and the Dexcom. Fingerstick readings can be within +/- 15% too, so don’t necessarily trust the fingerstick reading. But of course since it’s a blood-derived reading, you’re going to read a figure that you will read on the Dexcom in, say, 15 minutes. And that is why you want to calibrate during a nice and level BG state.

On your last question, you should see the devices that were the previous generation to this one, and then you won’t complain any longer! :slight_smile: I’ve done a 3 days trial with an early 1st-gen device which had the bulky sensor connected by a short cable to an even bulkier battery pack… ouch!

In a perfect world I’d like to have a sensor under my skin, without the need to change it every week. Maybe we’ll see this happen in a few years, who knows?

Cheers, Luca
Milan, Italy

P.S. Is your Dexcom calibrated in mmol/l? I don’t have this problem as in Italy we use mg/dl like in the US, luckily, but I was curious to see if the Dexcom has been localized for the UK.

Great advice Luca, Thank you!

Hi Chris, All the continuous blood glucose measuring systems have issues. I use the Dexcom Seven+ also. The Dexcon is amongst the best, but it’s performance varies by user and from sensor to sensor. Not everyone has the same experiences. That said most new users probably have higher expectations of accuracy and reliability than the system can deliver. Also the performance changes over time. When the sensor is first inserted under the skin a tiny wound is created which the body tries to heal. Blood flows to the area and an imune response occurs this takes time to occur and for the process to sabilize. The chemical composition and the structure of the fine teflon probe form a cell whose electrical characteristics change with the BG. Most users find the accuracy during the first day and a half is not the best. (But with good sensors the accuracy continues to improve.) The system has to adjust and entering the BG readings from your finger sticks calibrates the system. The system feeds the information into arrive at a calculated result that is not exactly the value that you enter. During the initial period the sensor may become confused and show ??? instead of a value. If this lasts longer than 3-5 hours you should contact Dexcom customer support. They will determine if the sensor should be changed. Dexcom is committed to having the sensor provide seven days of service. For a new user the first 24 hours can cause anxiety. My advice is be calm. Treat the Dexcom as additional information not primary information. Its strength is in sensing changes in your BG. The trends will suggest when it is time for a finger stick measurement and pehaps a corrective dose of insulin or glucose tablets. Personally I have experienced a high rate of sensor failures. Dexcom has graciously replaced them. So, when the sensor works that is fine. When the sensor fails I call support for a replacement. And if the sensor behaves in a quirky way, I contact support and ask that they download the data from my meter over the internet and ask for their evaluation. I have never had a situation where Dexcom said the sensor was good when I felt that it was not. I joke that the system is unreliable, inaccurate and ABSOLUTELY USEFUL. Now that I have lived with the system for two months, I understand how it helps me. I am a faithful user. Regards, Aaron

Regarding point 2, here are my findings. I have been on Dexcom since September 2009. I have some days where the Dexcom is accurate, and other days where it is way off. There are times when I calibrate that I am off by more than 100 units. I am adapting to that fact. I also find that my first 12 hour readings are not extremely accurate. I get alot of ???s on day one. Sometimes on day seven I get ERROR 1, and no readings. Despite these shortcomings, I am happy with my Seven Plus. I find the alarms most useful because I am hypoglycemic unaware. Before I had CGM, I would be at 35 mldl before before I felt anything. Now I get an alarm when I drop below 90 mldl.

It also helps me see how different foods affect my blood glucose levels. Yesterday and today my lunch was stirfried, and I discovered the meal didn’t affect my blood glucose levels for 2 - 2.5 hours, probably as a result of the high fat content. Knowing that will let me take my fast-acting insulin at the right time going forward.


Hi Luca
Yes the UK Dex is in mmol/l so 3 points difference is actually equivalent to about 50 in mg/dl. That is a lot!!

Hi Chris
I am using a Dex in the UK too. `i started a month ago, a few days before Christmas. Are you getting yours through Advanced Therapeutics?
The first 24 hours of a new sensor are not good for me. I had lots of problems with my first sensor and it only lasted 5 days, but I have figured out that this was a problem with the stickiness coming undone and the sensor moving about and not reading properly. I was plagued with ??? constantly.
As to accuracy. i find mine is very good if I have a steady bg. But after breakfast my bg shoots up no matter what i do and I get the double arrow warning to say my bg is rapidly rising. The Dex will read much higher than what my bg really is at this point. But once it stabilises again I put in another calibration reading and it sorts itself out.
I always do a calibration before I go to bed, that way it is good for 12 hours and won’t wake me in the night.
After a month i am probably still in the “need convincing” stage but getting better now that it is behaving better. After all I have shelled out nearly £1000 on it so I have to give it a good go right?
Good luck, we shall muddle on together

Hi Dee, Yes i bought through Advanced Therepeutics and yes costs lots of money but hopefully will help. Was really useful info about it being not so reliable when blood is rising quickly (i too have same thing of massive rise after breakfast followed by stability in afternoon. I tried the pump last year and didnt get on with it but feel more positive about this device although thought they could of made effort to at least blend it in with a persons body, guess this is of less importance though, thanks again for responding and good luck!

Thanks Rita!

Thanks Aaron, really useful advice and yes i have heard that the sensors are a little tempermental but am only 3 days in so will see. Is the sensor affected if goes into blood vessel or is this not poss due to how far it actually goesin?

Ah OK Dee, this is different then! Most people here speak about mg/dl and not mmol/l, and being the conversion rate 18, that is 54 points in mg/dl. Quite a bit, infact.

I am assuming that the clock and calendar are also localized, with the more common D-M-Y and 24 hours clock.

Thanks for the information, I bought my Dexcom in the US and am still ordering the sensors in the US.

Ciao, Luca

Hi Chris, I am not a doctor or a technician. I can only share my experience. I am overweight and so in my case the sensor rests in a fatty layer well over the musles. From reading the Dexcom manual they suggest finding a fleshy area and pinching the skin slightly. I don’t think this proceedure would allow to sensor to enter a sizeable blood vessel. From my experience, blood vessels are tough to pierce. When I go for blood work, the phlibotomist (yes that’s what they call the people who draw the blood) needs to catch the vein just right or the vein moves aside. So I would not worry about this. AaronM

You are correct about becomming hypoglycemic aware. I had one very frightening low BG episode after very vigorous excercise. Afterwards, I cut way back on excercise and used to aim at BG no lower than 100. With the Dexcom I feel more comfortable in shifting my range much lower. I set the low alert at 70. While the absolute BG values are not always accurate the direction alerts with the arrows are much better. Now I feel much more comfortable trying to keep my BG in the 70-95 range as much as I can. Also I am more aggressive in using short acting insulin if my BG is still high after meals.


Hi, You mentioned your steep rise in BG post breakfast. Byetta in conjunction with one of the sulfonylurea class drugs is very effective in preventing post meal peaks. You may want to check with your doctor. Byetta is very powerful and works independently of insulin.


High Chris! Let me respond to the 3 original questions:

  1. As Sarah explained really well, the alarm goes off when Dexcom has gone ??? and “doesn’t know what to think” anymore, OR it’s been 12 hours since your last bG entry. One thing which she didn’t say, but a lot of us “feel to be true”, is that Brand new New Sensors should be calibrated a lot more frequently on day one and day two. They’re still “breaking in” and changing a lot, the Sensor voltage versus bG curve become a lot more stable after it’s been in for a few days.

  2. Dexcom is absolutely, positively NOT !!! as accurate as traditional fingersticks. If you have any doubt about the accuracy of Dexcom’s value (e.g., feeling like “3” while it’s saying"6"), poke IMMEDIATELY.

You should never expect Dexcom to have good values if you’ve (maybe) been sleeping with it squashed against the bed. There will have been poor blood circulation near the Sensor wire (“pooling” and “squished right out, never refreshed” are BOTH possibilities). Bad blood circulation causes “stale” ISF, and stale ISF makes bad readings. If it’s gone “stale”, your ISF won’t be fully freshened until you’ve been up and active for at least 1/2 hour. Don’t enter a conflicting fingerstick as a “calibration” value during this time-- the Dexcom’s voltage levels will still be wrong from the “stale” ISF, and you’ll wreck the calibration curve. Just use the fingerstick value to guide your activites, and enter a fresh poke as a calibration later in the morning.

  1. Although your photo indicates that you could be in a “dating” stage of life, I can’t resist making a joke at your expense-- Is this “a problem” because you’re currently working as a professional male stripper?

Dee, if you can anticipate that “I’ll probably be needing a new one tomorrow,” you can shoot in the new Sensor 12-24 hours early-- and just leave the Transmitter in the old one, still running.

Upon startup, the Sensor has actually had a full 24 hours “warm-up”, and you’ll be avoiding the “first day” accuracy problems. I do this-- although I can get 14-16 days from nearly every Sensor, I shoot in the replacements on the night before day 13 begins, and then move the Transmitter and execute the 2-hour countdown during mid-morning, after any wake-up and breakfast bG weirdness has quieted down.

Dexcom nearly always reads late. And there are simple reasons why reasons why it will typically be MORE late at tracking “rising” bG, than it will be during "falling bG. I’m not medically qualified to offer any opinions, but I’d like to SWAG (as “just another unqualified user”) that your bG really is going up, really sharp… but by the time Dexcom gets starts showing this, you have ALREADY PEAKED and turned back downwards. Dexcom still shows the rise continuing, while your insulin dose has taken over, and begun working strongly.

BUT, I feel that there’s also a real problem here: The tissues in your body are largely “fed” by ISF, not directly exposed blood cells. So nearly everywhere, arteries and veins excepted, the sudden rise in glucose levels really is present-- and it’s maybe damaging for body tissue. If I were seeing your bG and Dexcom patterns, I would try to “smooth out” the

Thanks Rick, Am flattered by the male stripper job prospect but think the sight of sensor might put off a few of those drunken ladies from leaving cash in my thong!!
Yep, like to thinks there is still a bit of life in this fast approaching (if not already there) middle age dog but apprecaited good advice - especially about the circulation issues if sleeping on stomach which i do. Surprising what you mention about Dexcom not being as accurate, started dexcom this week and rep categorically said the plus was more accurate - guess he had other agenda though i guess. Just quick question, is it poss you could insert sensor into blood vessel as you can by shots or pump or does it not work same way? Also interested in how u can max sensor use, rep mentioned i can simply go into start sensor and press and will extend, is it that simple??