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[Equipment] How accurate is the Wellue O2 Ring?
How accurate is the Wellue O2 Ring?
Hi folks

I'm unsure whether I should be starting a new thread for this. I read the plea in the sticky thread about keeping everything in one thread, but this isn't really related to the thread I started a few days ago -- it's more a general question. So I'm really not sure where/how to post it. Perhaps somebody will be kind enough to let me know if I'm doing the wrong thing?

My question is about the accuracy of the Wellue O2 Ring, which I have, and which I can see that a number of other folks have as well. It seems to be a popular piece of equipment.

I also have a calibrated, hospital-grade [pulse oximeter which, unfortunately, does not record (well, it does, but it needs proprietary stuff to get the data out). I find that my Wellue O2 Ring over-reads the hospital-grade oximeter by 1-3 percentage points, in all circumstances in which I can I compare them. I can't compare them when I'm asleep but the discrepancy is there when I'm sitting down, lying down, exercising, etc.

I don't know which of these machines is "right", if either is. The Wellue was much cheaper than the hospital unit, but it's a more modern design. Also the Wellue has a much more snug, repeatable finger attachment.

Does this small discrepancy matter? It probably doesn't when the question is whether your SpO2 is 95% or 98%, but it might do when it's a question of 91% or 88% (which is where I find myself).

Has anybody else looked into this? So far as I know, no fingertip pulse oximeter claims an accuracy of better than +/- two percentage points, which is what Wellue claims.

Best wishes, DS
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RE: How accurate is the Wellue O2 Ring?
I can't say as to which one os more accurate but I notice the same thing with mine.  I have both the Wellue (Sleep U) and the Contec CMS50F (older version).  The Wellue always reports about 2%-3% higher values than the Contec.  Never have figured out if it is just the difference in how each unit calculates the numbers, or if it's a difference in the style of sensor.  
I seem to recall that Wellue calculates their numbers differently which may explain the discrepancy.  Something along the lines of the unit displays stats in 1 second increments but the software only uses 4 second increments.  But my memory isn't what it used to be.......

Your Dr should have a calibrated unit in their office.  Next time you go bring both units with you and see which of the two match the Dr.
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RE: How accurate is the Wellue O2 Ring?
This might be best off in the Software forum, but unfortunately, I can't move it. I'm sore a moderator will if necessary. Smile

I suspect it might be a difference in how it's measured. The Viatom products are correct to +/- 2%, or 3% at <80% saturation. That said, it measures your saturation every second, then averages it over the last four readings, to give you the reading it displays/saves. So I would expect it to perhaps looking slightly different. I actually recorded this overnight, wearing both a viatom product on one hand and the contec product on the other. Overall, the general results lined up pretty well for me, and I didn't see a lot of difference. Even if individual points were different, or one was a little behind the other (and I genuinely can't remember which was which now or if they swapped), the averages were the same, the line of the graphs was the same, the proportions at each group of measurements was close enough to be of no statistical difference.

Without actually testing them, it's going to be hard to know which is more "accurate" and even then, ALL Pulse oximeters are only an "estimate" of oxygen levels because they are all based on assuming a certain level of tissue perfusion, extraneous light, dehydration, etc. The ACCURATE way to test is via a blood gas measurement (and even then, if they use the arterialized capillary blood gas from your earlobe rather than the traditional arterial blood gas from your wrist, then the oxygen measurement can vary by 5% from reality, at least according to the nurses on the ventilation ward I was in during November).

That said, I am entirely comfortable with them being reliable enough for at-home monitoring, and that SAME ventilation clinic that I was in? They use Viatom CheckMe O2 pulse oximeters on the wards and to give out to patients to monitor over two nights before planned admissions etc.
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RE: How accurate is the Wellue O2 Ring?
(01-03-2022, 10:14 AM)Ratchick Wrote: The Viatom products are correct to +/- 2%, or 3% at <80% saturation. That said, it measures your saturation every second, then averages it over the last four readings, to give you the reading it displays/saves. 

I think +/- 2% is a basic limitation of the technology. My understanding is that pulse oximeters cannot be calibrated in the sense that, say, a weighing scale can; when a hospital-grade oximeter is sold as "calibrated", all that means that it has been checked to produce results within the claimed 2% range.

My GE Medical unit, which cost five times as much as the Wellue, still only claims +/- 2%.
Nevertheless, I've noticed that some devices do read consistently higher or lower than others, and that's what makes me wonder if the Wellue is a "high-reading" device in general, or whether it varies from unit to unit.

As you observe, most of the clinics I've been in use cheap mass-market pulse oximeters, on the basis that they are just as "acccurate" as the expensive ones.

Problem is -- if a unit can over-read by 2%, that means that the 90% periods my wellue reports during the night could, in fact, by 88% periods. Does the matter? I really don't know.

Best wishes, DS.
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RE: How accurate is the Wellue O2 Ring?
I mean, yes... it could mean that. But it could also mean that your 90% periods were also 92% too. In general, it usually wouldn't matter, but because you are having issues where your sats are so close to the line where it really matters, that might be something to bear in mind (and maybe mention to your doctors when displaying that data). For me, personally, it makes very little difference, though.

From the reading I've done, there is a likelihood of cheaper oximeters giving either falsely high readings or simply missing desat events because they don't measure accurately. However, even expensive oximeters only have a certain "shelf life" so after that time, you might find that it's less reliable. So something like a Wellue/Viatom or Contec device might not be appropriate for someone who needs intensive monitoring, but for looking at overall trends at home, for something like OSA, it's probably "good enough".

As an aside, I guess that you can always use the data from the O2 Ring and work out how the data would look if it were 2% lower: export the data as a CSV, open in whatever spreadsheet app you use, then take 2 off the values in the SpO2 column etc. A few quick calcs would give you a <90% value. I really ought to make a spreadsheet or something to do this stuff automatically, instead of faffing around manually each time I want to check something...
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RE: How accurate is the Wellue O2 Ring?
I think it would be helpful to show a pic or a link to the O2 ring. It's seemingly appears to me these rings are more of gimmick than a consumer medical diagnostic tool.

Today I received an email from the YouTube CPAP drama queen and sensationalist Nick, from Australia promoting the Wellue O2Ring Wearable Sleep Monitor [https://sleepgadgets.io/review-wellue-o2ring/]. The only review I found was from that site linked which reads (to me) like an ad.

Put another way, if Apple could modify their watch to include [accurate] overnight SpO2 monitoring they'd sell even more watches. Right now it only provides a reading on demand.
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RE: How accurate is the Wellue O2 Ring?
Generally speaking...

Can a pulse oximeter be inaccurate?

Several factors can affect the accuracy of pulse oximeters, including poor circulation, skin temperature, skin thickness, current tobacco use, use of fingernail polish, and dark skin pigmentation, the FDA said. Recent reports have found that Black patients may not receive accurate readings from some oximeters.

How can you tell if a pulse oximeter is accurate?

The SpO2 reading should always be considered an estimate of oxygen saturation. For example, if an FDA-cleared pulse oximeter reads 90%, then the true oxygen saturation in the blood is generally between 86-94%. Pulse oximeter accuracy is highest at saturations of 90-100%, intermediate at 80-90%, and lowest below 80%.

Do pulse oximeters need to be calibrated?

Pulse oximeters do not require a zero calibration because the design incorporates continuous automatic zero calibration. Gain calibration is not required because the measurement technique does not require gain accuracy. A brief review of pulse oximetry theory shows why this is possible.

A little reading... 

Pulse oximetry theory and calibration for low saturations

Racial Disparity in Oxygen Saturation Measurements by Pulse Oximetry: Evidence and Implications
"The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane." -- Marcus Aurelius
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