Troubleshoot: 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 notice low glucose levels within the first 48 hours of applying your sensor, it's likely going through its calibration period. More on this topic here: Troubleshoot: Extreme High/Low Readings During First 48 Hours
  • Nighttime dips: t's natural for blood glucose levels to drop during sleep when our energy requirements are lower, especially during REM sleep. Pressure-induced sensor errors from laying on the sensor can also produce 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 a reactive hypoglycemic response, which is an exaggerated insulin response to a high carbohydrate meal, causing insulin to overshoot and decrease glucose levels rapidly, leading to a dip in glucose after a meal.
  • Measurements taken when your glucose is actively changing: All CGMs estimate blood glucose levels based on glucose in the interstitial fluid - 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 exaggerate the delta between a CGM reading and a finger stick reading when glucose is fluctuating rapidly such as after a meal or a workout. Therefore it's best to compare levels when glucose is most stable, in a fasted state or 2-3 hours after a meal.  
  • Accuracy margin: The gold standard for sensor accuracy is a blood draw measurement. 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 fleshier part on the back of your arm in the river between the 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 occur from time to time. If it feels 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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