Remember this? Well now we’ve a few measurements to try and figure out how well it really works. It’s only a few, as Ketone test strips are not readily available and are also quite expensive.
Obviously as an Interstitial Fluid based sensor there are going to be differences compared to blood tests, but what are they?
Firstly, it seems that CKMs are prone to the same compression problems as CGMs, which should be no real surprise. You can see this in the following image overnight where readings are lost.
From a measurement perspective, values are noticeably different with ketones present. The blood tends to be considerably higher than the sensor reads.
Conversely, when at lower levels, it’s a bit of a mixed bag.
It’s worth making the point that I have no frame of reference with which to calibrate this, as I’ve seen very little literature that looks at comparison of ketones in blood compared to in interstitial fluid.
There seems to be one paper available that has compared interstitial and blood ketone levels.
It indicates that in their experimentation, ketones in ISF are generally found at higher levels than in blood, and that they could be used as an early indicator of DKA. That’s obviously not what I’ve observed in the behaviour of these particular sensors, where blood levels are showing as higher than the readings I’ve got from the sensors.
There’s not a lot that we can take from this. Firstly, the device isn’t being sold as a medical device. It’s purely marketed for consumers to get an indication of whether they are in ketosis, and I think it works well enough for that.
But as an alternative to fingerpricks for ketones? At this stage I’d say no. Given the details the paper mentioned outlines, it isn’t aligned with how ketones seem to work, based on the available knowledge so far.
And there’s no real data related to this device. Whether that’s how it tracks ketones, how it’s calibrated, or any trials they’ve done.
So all in all, use it for determining your state of ketosis when following a ketogenic diet.
Don’t use it for anything medical. There’s something not quite right in that respect.