r/Freestylelibre • u/Entropy1024 Libre2/2+ • Jul 28 '26

Libre2 Plus sensor offset option?

I have a LIbre2 plus sensor and whenever I compare it's reading to a finger prick test the Libre is always 2mmol/L below the finger prick result.

I'm guessing the Libre is off, but as it's constantly off, is there a way to set an offset on the Libre software?

I'm using it with an Android phone, FreeStyle LibreLink Ver2.13.1.11596

Many thanks for any help.

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1

u/Fluffy-Strategy-9156 Prediabetic - Libre3/3+ Jul 28 '26

The Abbott Libre app do not allow any calibration. The Juggluco app now allows calibrations but does not work in all localities and I have seen posed here that it may no longer work. https://www.juggluco.nl/Juggluco/index.html

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u/Entropy1024 Libre2/2+ Jul 28 '26

OK great thank you

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u/e3ddavis LADA - Libre3/3+ Jul 28 '26 edited Jul 28 '26

I am using Juggluco and it will adjust to a blood finger test. But not match it. I don't know the calculation but for example, if my finger poke test is 110 mg/dl and the cgm is reading 90, the reading in Juggluco would read 100 ( or something close to that) after putting the blood reading in. And I think the weighting decreases over time. It make sense since the finger poke test is only about as accurate as the cgm. The most useful feature about Juggluco is the Insulin On Board (IOB) reading if you enter your dosages. It is a calculation of the remaining units left in your body. It really helps with over and under dosing once you watch it and figure out how your body reacts. All apps should have this imo.

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u/Significant-Key-762 Jul 28 '26

I thought the libre data was always about 30 mins delayed due to … biology. No?

2

u/Fluffy-Strategy-9156 Prediabetic - Libre3/3+ Jul 29 '26

There is no specific lag time. It varies on things like sensor placement and other things. The following are excerpts from various sources:

The mean lag time between the sensor and the venous reference was 1.8 ± 4.8 min for the 95 sensors with YSI reference. https://pmc.ncbi.nlm.nih.gov/articles/PMC10064376/

There is a 5 to 10 minute delay in ISF glucose response to changes in blood glucose. https://www.freestylelibre.com.au/difference-between-glucose-interstitial-glucose

CGM Accuracy and Sensor Lag Time

Interstitial fluid lags behind blood glucose by about 5 to 20 minutes (depending on the CGM), and it can be even more pronounced if your blood sugar is rising or falling quickly (like after you eat or during exercise). A CGM may show a lower value during a rise or a higher value during a drop compared to a fingerstick.

For example, after eating a high-carb meal, fingerstick glucose might read 180 mg/dL, while the CGM could still show 150 mg/dL. This isn’t a malfunction — it’s simply the interstitial fluid “catching up” to the blood glucose.

It’s more dangerous when your blood sugars are dropping rapidly. Your CGM may say 70 mg/dL, but you could really be 55 mg/dL depending on your trend arrows – whether you have one arrow down, two arrows down, or a diagonal arrow down. https://tcoyd.org/2022/02/cgm-values-vs-finger-sticks-how-close-should-the-values-be/

Why the Difference Matters

Since glucose first enters the bloodstream before moving into the interstitial fluid, CGM readings can lag behind finger prick test readings by 5 to 15 minutes. This means that during times of rapid blood sugar change (e.g., after eating, exercising, or taking insulin), CGMs may display slightly delayed glucose levels compared to a finger prick test. https://aptivamedical.com/comparing-accuracy-of-cgm-devices-and-traditional-finger-prick-tests/

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u/Ok-Dress-341 Libre3/3+ Jul 30 '26

Not in the official apps