Compression Lows

“Low alarms are happening a lot during sleep. I’m concerned about all these low sugar readings. Why is this happening, and can anything be done about it?” 

The FIRST priority is to confirm whether you are having a true low glucose event.  

• Do you have symptoms of low blood sugar? Ask, “Do I feel anxious, hungry, shaky, light-headed or confused? Am I sweating along with any of these symptoms?”
• If you have symptoms of low blood sugar and your monitor reads below 70 mg/dL, then treat with the Rule of 15.
• If you have no symptoms and feel fine:
  • Check blood sugar on a blood glucose meter. Does the meter reading agree with the sensor reading (within 10-15 points/mg/dL)?
  • If BOTH the sensor and meter readings are less than 70 mg/dL:
    • Use the Rule of 15 to treat low blood sugar properly.

I feel fine and my meter reading is above 70 mg/dL. What is causing the alarm?

Compression lows are false low-glucose readings on a continuous glucose monitor (CGM) caused by pressure on the sensor, often while sleeping. It is important to note that compression lows are an artifact of the current state of CGM technology. They are not a sensor malfunction, nor unique to any single CGM brand.  

The sensor filament does not measure blood. It rests in the fat layer just below the skin surface. It measures glucose in the fluid surrounding these fat cells. This fluid is known as interstitial fluid.  

Pressure on the sensor reduces flow of interstitial fluid and causes the sensor to read lower than your actual blood sugar. It temporarily “squishes” fluid away from the sensor filament, causing temporary fluid reduction and with that, a temporary drop in how much glucose is present for the sensor to measure.  

On the sensor glucose graph, a compression low appears as a rapid, steep drop in the graph line accompanied by a sharp decline in glucose numbers. This is followed by a quick rise once the pressure is removed, such as by sitting up, standing or repositioning.   

A low or urgent low glucose alarm will be triggered when sensor glucose value drops below the low alert threshold in the CGM alerts settings (the default setting is 70 mg/dL). The default urgent low glucose alarm will be triggered if the glucose value dips below the urgent glucose safety alert threshold at 55 mg/dL.   

But – the person wearing the sensor feels fine, without the shaky, hungry, light-headed sweaty or confused symptoms of low blood sugar. This is because blood glucose is normal. The sensor is giving an alert due to glucose in interstitial fluid being temporarily diverted away from the sensor filament.   

Compression “lows” occur most often during sleep or when lying down. They can also be caused by tight clothing, elastic bands, weighted harnesses and blood pressure cuffs.  

How to Prevent and Manage Compression Lows

• Confirm with a Fingerstick: If a low alarm goes off but you feel fine, check your blood sugar with a traditional glucometer before treating for low blood sugar. 
• Avoid Over-Correcting: Change position to release pressure and wait 5-10 minutes to see if the sensor reading rises back to normal before consuming food or drink. Consuming carbohydrates for a compression low can lead to high blood sugar hours later.
• Sleep Adjustments: Use a small pillow to prop yourself up or try to sleep on your back.
• Alternative Placement: Talk to your doctor if alternate sensor site placement may be right for you.
• Avoid tight clothing or elastic bands over the sensor.
• Protective Barriers: Some users report success using protective covers or barriers, modifying the area around the sensor to distribute pressure.

Common Pressure Distribution and Protection Devices

• Adhesive Overpatches: These are adhesive, often waterproof patches that fit over the sensor, securing it to the skin and distributing surface tension more evenly.  
  • Ensure the patch or cover is specifically designed for your CGM as the sizes differ.
  • Never cover the vapor vent on top of the Freestyle Libre 3 Plus sensor, as this will trap moisture and could weaken skin attachment.
• CGM Covers/Shields: Rigid or semi-rigid plastic covers are placed over the sensor and distribute pressure from accidental bumps or pressure during sleep across a wider area, preventing direct compression on the top of the sensor.
• Adhesive Patches with Foam Padding: Some patches include a small, soft foam ring or pad that surrounds the sensor transmitter to provide cushioning and redistribute localized pressure.
• Armbands/Wearable Bands: Soft elastic bands that are worn over the CGM hold it in place and reduce the risk of it being knocked off, while also distributing external pressure.

When in doubt: A fingerstick confirms whether your glucose is truly low. It takes ten seconds and removes the guesswork.

References

1. S. Y. Kwon, J. S. Moon. Advances in Continuous Glucose Monitoring: Clinical Applications. Endocrinol Metab (Seoul). 2025 Apr 8;40(2):161–173. doi: 10.3803/EnM.2025.2370 
2. G. Mongegranco. CGM Is Reading Low Values at Night: Causes and Solutions. University of Michigan. Retrieved from: https://teamdynamix.umich.edu/TDClient/210/DepressionCenter/KB/ArticleDet?ID=10689 
3. Compression Lows vs. True Low:  How to Tell Them Apart. https://www.snaq.ai/blog/compression-lows-cgm-v-shape-pattern 
4. American Diabetes Association Professional Practice Committee. Introduction: Standards of Medical Care in Diabetes—2022. Diabetes Care. 2022;45(Suppl 1):S1–S2. 
5. Mensh BD, Wisniewski NA, Neil BM, Burnett DR. Susceptibility of interstitial continuous glucose monitor performance to sleeping position. Journal of Diabetes Science and Technology. 2013;7(4):863–70. 
6. American Diabetes Association Professional Practice Committee. 7. Diabetes Technology: Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S126–S144. 
7. Bailey T, Alva S. Landscape of Continuous Glucose Monitoring (CGM) and Integrated CGM: Accuracy Considerations. Diabetes Technology & Therapeutics. 2021;23:S-5.