Troubleshoot: Low Glucose Readings


This article provides an overview about why a typically healthy individual may experience low glucose readings.

About Low Glucose Readings

It's not abnormal for people’s glucose to intermittently dip below 70mg/dl. In one study of healthy individuals wearing CGM, 41% of people experienced glucose levels less than 70 mg/dL in a 24-hour period.

A few other reasons you might be seeing low readings:

  • Calibration period: If you're seeing abnormally low glucose levels within the first 48 hours of applying your sensor, it is likely that your sensor is still going through its calibration period. You can read more on this topic here: Troubleshoot: Extreme High/Low Readings During First 48 Hours
  • Nighttime dips: It’s natural and normal for blood glucose levels to drop during sleep. Since our energy requirements are lower, the body requires less glucose to perform usual physiological processes, especially during REM sleep. There’s also a chance that low nighttime glucose level readings are the result of pressure-induced sensor errors from laying on the sensor - which may cause false low readings. Our blog post here has more info on low nighttime readings.
  • Post-meal lows: Glucose dips below 70 mg/dL that occur just after a post-meal glucose spike may indicate reactive hypoglycemia; which is an exaggerated insulin response to a high carbohydrate meal, causing an overshoot in the amount of glucose that is absorbed out of the bloodstream and into cells, leading to a dip in glucose after a meal.
  • Measurements taken when your glucose is actively changing: The FreeStyle Libre is factory-calibrated to estimate blood glucose based on interstitial glucose - which is the fluid between skin cells. These numbers can lag behind blood glucose levels by ~15 minutes depending on how quickly things are changing. This can stack up especially during times of actively changing glucose to produce a delta between finger stick and CGM reading.
  • Accuracy margin: The gold standard for sensor accuracy is a blood draw measurement and all at-home glucose monitors have error margins (MARD) to that standard. Finger sticks tend to be in the range of 5-10% MARD, while the FreeStyle Libre CGM has a MARD of about 9.7% over 14 days. Since all readings fall within an error margin, two sensors might read ~15% differently. 
  • Location: The exact spot can vary from person to person, but we generally find that the best location is on the back of your arm in the river between triceps and shoulder muscle. We've noticed higher failure rates when the sensor is placed over a muscle.

This all being said, unfortunately, sensor errors do occasionally happen. If it seems like that's the case, please reach out to the Levels Support team at and they'll be happy to help further!

Further reading:

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