What Causes This?

I was at day 10 of a G5 sensor and everything stable in the 90s.

All of a sudden dropped 13 points and 5 minutes later increased 10 points. Then became stable again and two days later still ok. Was sitting on the couch so not compression. What can causes these sudden changes in readings?

I understand that the sensors use an enzyme that is applied to the sensor tip and that the enzyme interacts with components in the interstitial fluid that are analogous with blood glucose and produces an electrical signal useful to the Dexcom algorithm.

As that enzyme gets used up it may cause noise like you describe. Since it happened on day 10 it makes this possibility more likely. Having said that, some sensors can produce great looking lines for far longer. I’m not sure what the magic ingredient is in that situation.

When I start to see that kind of noise, it’s the first indication to me that the sensor is starting to fail, although it can go many days before the data becomes unacceptable.


Thanks Terry. I have not see the word “noise” on Xdrip yet and the sensor is still working well but I will be ready to soak a new sensor as soon as I see “noise” or the readings become off.

Could it possible be that any time blood is not perfectly uniform throughout our body and it could just have been an unusual reading because of this?

Noise sometimes resolves itself. If pushing a G5 well past 7 days, persistent noise is a hint that it’s time to retire it.

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Thanks Dave, I used to think noise was interference but now know it the the sign of a sensor starting to go. This one was cause if concern when it went down thirteen and up 10 but it has lasted three more days and still very good readings. I think I’ll interpret persistent as half an hour.

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Here’s an example of a noisy, yet still useful, line:

Screen Shot 2020-02-15 at 9.45.23 AM

And one without much noise:

Screen Shot 2020-02-15 at 9.45.34 AM

I understand that blood sugar does not make big jumps in the short term. Going up 15 mg/dL in five minutes and then dropping 13 mg/dL five minutes later doesn’t happen naturally. It is an unfaithful recording of events and the general term, noise, is useful here.

I think that blood glucose is never 100% uniform throughout the body, but this is not the cause of the sensor reading jumpiness or noise.


Correct: “noise” isn’t interference. It refers to one or more data points that went in the wrong direction or suddenly moved a large amount–more so that interstitial fluid glucose values would generally move. Noise is very well illustrated by the first graph that Terry4 posted.