What are the causes of signal loss with Dexcom (Continuous Glucose Monitoring) devices?

Causes of Signal Loss with Dexcom CGM Devices

Signal loss with Dexcom continuous glucose monitoring systems primarily results from technical sensor failures, physical distance between sensor and receiver, calibration errors, and interference from certain medications or physiological conditions, rather than true "signal loss" in the traditional sense.

Technical and Device-Related Causes

Sensor Failure and Malfunction

• Sensor failure is a recognized technical issue that can interrupt data transmission and is documented in FDA adverse event databases, though specific rates are not consistently reported across manufacturers 1.
• The main source of error in Dexcom sensors is the calibration process itself, not signal transmission—calibration with patient measurements versus reference measurements can increase mean absolute relative difference from 8.5% to 16.0% 2.
• Sensor accuracy varies by placement location, with posterior upper arm placement showing better performance (8.7% MARD) compared to abdomen (11.5% MARD) or upper buttock (11.2% MARD) 3.

Physical and Environmental Factors

• Physical distance between the sensor and receiver/smartphone can interrupt data transmission, though this is a practical limitation rather than a sensor accuracy issue (general medical knowledge, not directly cited but implied by device operation).
• Sensor wire trauma and insertion site issues can affect performance, though Dexcom G4 and later versions reduced wire diameter to minimize this problem 1.
• Low oxygen states can affect glucose oxidase-based sensors, though Dexcom's proprietary system was specifically modified to reduce impact from low oxygen conditions and operate at high signal-to-noise ratio 1.

Medication and Substance Interference

Older Dexcom Models (G4 and Earlier)

• Acetaminophen causes significant interference in older Dexcom models—ingestion of 1g acetaminophen resulted in CGM measurements ranging from 85 to 400 mg/dL while plasma glucose remained at 90 mg/dL 1.
• Other interfering substances in G4 Platinum include ethanol, albuterol, lisinopril, atenolol, atorvastatin, and wine 1.

Newer Dexcom Models (G6 and G7)

• Dexcom G6 largely eliminated acetaminophen interference through a perm-selective membrane coating that inhibits diffusion of pharmacologic spurious signals—1g acetaminophen doses showed mean interference of only 3.1 (±4.8) mg/dL 1.
• Hydroxyurea causes falsely elevated sensor glucose readings that are discrepant from actual glucose values, requiring additional blood glucose monitoring when this medication is used 1.
• Mannitol and sorbitol administered intravenously or in peritoneal dialysis solutions cause falsely elevated sensor glucose readings 1.

Physiological and Patient-Related Factors

Skin Reactions and Adhesive Failure

• Contact dermatitis (both irritant and allergic) can necessitate sensor removal, interrupting continuous monitoring 1.
• 2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate (MBPA) in the newer Dexcom G6 adhesive (changed in 2019) has caused increased severe skin reactions requiring sensor discontinuation 4.
• Isobornyl acrylate, a known skin sensitizer, can cause spreading allergic reactions that prevent continued sensor use 1.

Special Populations

• In advanced chronic kidney disease, sensor accuracy may be reduced, though Dexcom's modified glucose oxidase system performs better than other CGM technologies in this population 1.
• In ICU settings, Dexcom G7 shows slightly higher mean RAD (16%) compared to outpatient labeling, though no correlation exists with severity of illness 5.

Data Gaps and Reporting Issues

• Data skips should not exceed 30 minutes at a time for proper clinical use, though specific causes of these gaps are not well-characterized in the literature 6.
• Sensor performance requires wearing the device >95% of the time for optimal accuracy, and gaps in coverage compromise diabetes management 7, 6.
• Time lag between interstitial and blood glucose is minimal—average sensor time lag is only 5.7 minutes, contrary to earlier assumptions of substantial delays 2.

Clinical Implications

• Routinely review all medications and supplements to identify interfering substances, particularly hydroxyurea, mannitol, and sorbitol in current-generation devices 1.
• For older Dexcom models (pre-G6), advise patients to use confirmatory blood glucose monitoring when taking acetaminophen or other known interfering medications 1.
• Monitor insertion sites for skin reactions and consider patch testing if allergic contact dermatitis develops; implanted sensors may be an alternative for those with tape sensitivities 1, 4.
• Ensure proper sensor placement (posterior upper arm preferred when possible) and maintain physical proximity between sensor and receiver 3.