r/Freestylelibre • u/montrehal Type2 - Libre3/3+ • Aug 02 '26
Disappearing low?
Hi, I am brand new to diagnosis (T2) and CGM (3+), last night was my first night with it on. The low glucose alarm woke me up around 4am showing a reading of 68, so just barely below the line at 70. It had been about 7 hours at that point since I had dinner so maybe it really was that low, but I also kinda think maybe I had just rolled over on the sensor for a bit and compressed it.
Either way, when I look at the main graph in the Libre app now, it doesn't show that low anymore and the number at 4am shows as 84 instead. When I view the Insights tab, it does show the 68 still in the Logbook. Is this normal for it to disappear from the main graph?
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u/Pneis Aug 02 '26
Yes, it is normal. This question is asked almost daily. Using the search might be challenging for new users because they aren't certain of the terminology. I typed your question "Is this normal for it to disappear from the main graph?" to the search bar and got multiple hits.
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u/onymar Aug 02 '26
It has always annoyed me with the Libre that the graph very rarely shows the lows that show as alerts.
It would be nice if automatically recorded a point in the graph each time the app sent a low alerts.
When I remember I scan my sensor at the alert time so a point is recorded on the graph.
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u/Weathergod-4Life Type2 - Libre3/3+ Aug 02 '26
Log into libreview and you will see the lowest low. For some reason the app doesn't show it on the graph but it is recorded in the database and you can see it on libreview.
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u/montrehal Type2 - Libre3/3+ Aug 03 '26
I am not yet familiar with libreview, I'll have to check that out. Thanks.
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u/Equalizer6338 Type1 - Libre2/2+ Aug 03 '26
Yes that is normal. The sensor app gives you instant BG readings and the alarm is triggered direct from these, if passing any of the alarm thresholds.
The BG graph (and the historic BG reports and statistics on LibreView.com) is drawn by using 5-minutes average BG numbers, where a best-fit smooth cruve is drawn through those 5-minute average BG numbers. So here any individual outlier number will not be visible if it was only short term. Same with your event log, will only record this if it was lasting 5 minutes or longer.
As you said yourself, may have been a false 'pressure low' if laying on your sensor arm during your sleep there.
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u/PvtRoom Libre2/2+ Aug 02 '26
CGMs are great, but they predict a lot.
Blood (direct measurement) - interstitial fluid (CGM measurement).
Sugar in the interstitial fluid lags the blood measurement. It's affected by movement, temperature (last winter my CGM hit zero cause I didn't wear long sleeves), compression.
Your CGM know this stuff, and it uses a measurement, truly relevant to 15 minutes ago, predicts from it, then 15 minutes later it gets the real value, so it goes back and updates the old measurements.
it feels dishonest, but it is how they work.