T1D glossary

Compression low

Also called pressure-induced sensor attenuation, PISA, false low.

A compression low is a false low on a CGM caused by pressure on the sensor site, most often from lying on it while asleep. Researchers call it a pressure-induced sensor attenuation (PISA). It can trigger a low alarm, or make an automated pump stop insulin, when glucose is not actually low. (Baysal et al., compression lows, 2014)

Worked example

At 2:10 a.m. the graph drops from 120 to 58 mg/dL (6.7 to 3.2 mmol/L) in 15 minutes while the child sleeps on the arm with the sensor. They roll over, and within 20 minutes the line is back near 118 mg/dL (6.5 mmol/L). A fingerstick during the dip would read close to 120.

Related terms

• Continuous glucose monitor
• MARD
• Signal loss
• Closed loop

Sources, quoted

• Baysal et al., compression lows, 2014: “Another common problem, particularly overnight when a subject sleeps on their sensor, is sensor attenuation, which we will refer to as pressure-induced sensor attenuation (PISA).”
• Baysal et al., compression lows, 2014: “Miscalibration, noise spikes, dropouts, or pressure applied to the site (e.g., lying on the site while sleeping) can cause inaccurate glucose signals, which could lead to inappropriate insulin dosing decisions.”
• Baysal et al., compression lows, 2014: “These studies focus on the problem of pressure-induced sensor attenuations (PISAs) that occur overnight and can cause undesirable pump shut-offs in a predictive low glucose suspend system.”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.