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Dexcom One + wildly different readings to actual levels

A

anouser1

Active Member
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Hi all,

I started using a Dexcom One+ earlier today and so far I have had wildly different readings.

Before lunch, I had a Dexcom reading of 5.6 with a finger prick scores of 4.2 and just now I had a Dexcom reading of 8.4 with a finger prick score of 6.0.

Although these differences were without negatives, it seems dangerous that I could be on the verge of a hypo whilst Dexcom is saying I'm at a perfect level.

What is causing these levels? Is there a way to fix this? I have really good control anyway and if I'm going to have to constantly be checking for terrible readings anyway I'm struggling to see the point of using the Dexcom at all?
 
As a T2, I don't have the same concerns as T1s using this tech to avoid hypos but from my previous tests of continuous glucose meters (CGM) vs blood glucose meter (BGM) I have always found that for me CGM runs 1-2mmol/l higher than BGM. Right now my Freestyle Libre 2 reader BGM says 6.4, while Libre 2+ CGM says 7.8. Others see this reversed, with CGM reporting lower numbers than BGM.

There are different reasons for these differences. For example, the first 24 hours are usually a bit off while the sensor establishes itself and settles. The sensor's placement or the sensor itself could be the cause. Both CGMs and BGMs have an allowed margin of error and even if you did multiple BGM tests on the same blood sample with multiple test strips, you are likely to get different readings.

What can you do about this? Dexcom ONE+ allows you to calibrate the sensor with BGM reading. I'd try to calibrate it after it has settled in a day after insertion. Some pre-insert sensors prior to old ones expiring for improved precision upon activation. If you find sensor is consistently running higher, you could set your alarm to warn you sooner, e.g., at 5mmol/l instead of 4 to give you time to intervene before you hit hyp zone.
 
I get that all measurements have a margin for error, but being consistently above is just purely frustrating. What do you mean calibrate? I 've seen that I can log events such as a BG reading but how does this help?
 
Have you taken the lag between finger prick (blood) and sensor (interstitial fluid) into account? It takes 5-15 min for the blood glucose to reach the interstitial fluid and so a finger prick and sensor are not measuring the same thing at the same time - the sensor will follow the finger prick after a lag.

Check the senor reading after 5-15 mins to see if they match better. When BG is rising or falling rapidly the lag can result in differences of 2 mmol/L for me.
 
I find this after a hypo.
From what I’ve read interstitial fluid is the last in line. It’s a big scramble for when the sugar is back in the blood to “protect the brain” first?
It can take a good 40 minutes lag when the BG is “that” depleted..
 
I self funded Libre2 for a few months and found it accurate in the mid ranges but way out when my glucose was rising/ dropping rapidly.
I’m now self funding dexcom1+ and finding it more accurate overall.
Considering the margin for error in finger prick meters alongside the margin for error in the sensors I’m happy to accept the results as guidelines/trends for where my food choices are making impact on my health and wellbeing.
I wouldn’t calibrate the sensor on the first day while it’s settling in but have done so at other times with reasonable success. I’ve only needed to do that twice.
 
Interstitial fluid (ISF) could be seen as the last source of glucose that feeds the organs including the brain (arterial blood --> ISF --> lymph --> venous blood). The lymphatic system (the drainage) is very depleted of glucose but it doesn't matter as it doesn't play a role in supplying glucose.

The one issue I have is that during intense exercise, the muscles suck out all the glucose from the ISF and Libre artificially records a hypo that does not correlate with blood glucose, even after taking the lag into account. I've had 3.2-3.5 on Libre after exercise but glucometer was always >5.0 from start to finish.
 
I've used a dexcom g6 and now a G7. I believe the ONE+ is a pared down version of the G&, so my experience may be relevant.

Firstly, some sensors are very inaccurate for the first 24 hours while they "bed in" as irritation of the skin/tissues due to the sensor insertion can distort the bg result. In my case, that tends to make my sensors read low. This usually fixes itself within the first 24 hours but if not you can calibrate the sensor to your glucometer reading. Best not to do this for the first 24 hours though, as that can mean your meter will read high after your body has got used to the new sensor. (At least, that was the rationale I was given by dexcom support).

I insert my new sensor when I have reached the official end of an old sensor, but don't activate it till near the end of the 12 hour grace period. That way most of the wild inaccuracies occur while I'm still using readings from my old sensor.
 
Thanks for all of this. The ONE+ has shown me consistently around 6.0 for 3 hours now and yet still when I finger test, I get 5.1. I appreciate that 0.9 isn't the biggest difference but its still quite a lot less accurate. I've calibrated it a couple of times back down to correct levels but always ends up way higher.

I'll give it the rest of this 10 day cycle as I'm almost 24 hours in now but if it continues to be that much higher to the point that I'm finger testing constantly to recalibrate it, I'll just stop using it as there's no upside.
 
I wouldn’t disagree..

I’ve seen some crazy results on a sensor arm, just hand sawing timber?
 
There certainly doesnt seem to be any upside as far as cost is concerned, if self funding. It appears the price, per day, is near identical to the Freestyle Libre which I have been using, on and off, since they first came onto the market. Price fixing? It wouldnt surprise me.
 
Been told today by my DSN that I should be changing over to Dexcom one+ towards the end of the year. Currently using the Dexcom one.
 
If you go for 1 or 3 months subscription for Dexcom ONE+, there is a discount compared to Libre 2/2+. Made an order last week, working out how to combine data across the two manufacturers so that I have my stats while I fully transition over to Dexcom.
 
Dexcom has the facility to calibrate your readings, go to Settings, go down to Calibrate you can there enter your finger prick reading. The system will then make adjustments accordingly. I have found it's a powerful feature to this system. I've only been using these auto systems for 4 years but find that the siting of the sensor can give differing readings.
 
I use the Dexcom One. It takes at least 24 hours to settle and start reading accurately with a new sensor. I finger prick within this timeframe. I use X-drip so am able to add calibrations after 24 hours have passed. Dexcom One is really accurate and my blood sugar management is so much easier and less stressful so I would not go back to using the LIbre.
 
If you use Shuggah app it supports readings from both Libre and Dexcom CGMs so you can use either and see data in one place. It also syncs with Apple Health if you are an iphone user
 
I have not used Dexcom but have used Libre since they were first introduced into Europe (before USA!). The basic technology is the same. You can read it in the hundreds of pages of the patents. The major difference is in so called calibration and smoothing. Both systems rely upon a foreign body being inserted below the skin level to measure glucose within the interstitial fluid that surrounds all our cells, including the brain cells. IMHO That is the bit that really matters.
With both systems the body reacts to the foreign body by producing large cells, macrophage, that coat the foreign body and attempt to protect us from the invader. Those large cells use up glucose! But everyone is different. We all react differently to a simple cut or abrasion. Manufacturers try to estimate a particular persons reactions, but it is little more than an intelligent guess particularly soon after first insertion.
They also try to smooth wild variations
Spot checks of individual readings are not well smoothed which is why trends are so much more use, particularly during early days.
So how does this affect Libre v Dexcom?
Libre is preprogrammed with expected curves while Dexcom allows adjustment to fingerprick levels.
Problem with the latter is that it is just an individual level at one moment in time.
It can be wrong. Even the strip manufacturer says only within a few percent for 95% of the tests, at best!
Doctors are warned that even large sample tests in the lab using very experienced testers and expensive equipment have substantial variation.
Airplane pilots, responsible for perhaps hundreds of lives, are not allowed by their licence to use fingerpricks to test their glucose. The must use CGM if taking insulin.
That is mainly because all CGM rely upon many many single readings to provide a much more accurate average and trend.

So can you rely upon a single 25c strip and single drop of blood?
That is why I use Libre rather than Dexcom. But Libre still needs intelligent interpretation.

I will try to show graphs of spot checks against the average trend, both at the start of sensor and at the end. The variation at the beginning when the body is still reaction to insertion is enormous. Much more than a few ml/mol. Taking spot checks at this time is both dangerous for precise treatment and calibration. We have to intrepret readings. We have to understand variation.

Attached is A sensor just installed - the yellow line is continuous spot readings - the red line is the smoothed averages of the trends- and the same sensor after 14 days- readings much more reliable with little variation- but even this one shows a false spot low warning at around 9:30.

 

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And the advice to Doctors - you can choose Glucose and also hba1c - and see how great the variation is for professionals using large samples, experienced technicians and very expensive equipment. Do you really think you can do better with a single finger prick?

Your results may vary: the imprecision of medical measurements

### What you need to know Clinicians and patients need to interpret a multitude of medical measurements. These are often central to monitoring health and informed decision making. Has the serum cholesterol concentration come down since starting a statin? Have vitamin D levels gone up? Is the...
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I you have only started using it today there is always a 20% difference between Dexcom 1 and your finger pricking score for the first 24 hours. You will rarely get them matching after 24 hours. Dexcom is really good for using when you are travelling or not in a suitable place to finger prick.
 
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