What should be included in the special instructions for a patient using a medical device sensor as prescribed?

Special Instructions (SIG) for Continuous Glucose Monitor Sensor

When prescribing a CGM sensor, provide comprehensive written and verbal instructions covering device application, calibration requirements (if applicable), data interpretation, troubleshooting, and backup blood glucose monitoring procedures. 1

Initial Patient Education Requirements

All patients receiving a CGM sensor must complete structured education and training before first use, covering both technical operation and clinical interpretation of glucose data. 1 This education should occur either in-person or remotely and must include:

• Proper sensor insertion technique and site rotation to minimize skin reactions 1
• Understanding of sensor warm-up periods and when readings become available 1
• Recognition that interstitial glucose measurements lag behind blood glucose by 5-15 minutes 1
• Interpretation of trend arrows and their clinical significance 1

Device Application and Maintenance Instructions

Apply the sensor to clean, dry skin on recommended body sites (typically abdomen or upper arm depending on device), rotating sites with each sensor change to prevent skin irritation. 1

• Avoid areas with scarring, lipodystrophy, or active skin conditions 1
• Monitor insertion sites regularly for contact dermatitis, which has been reported with all skin-attached devices and may be linked to isobornyl acrylate sensitivity. 1
• If skin reactions develop, consider patch testing to identify specific allergens and consult resources at pantherprogram.org/skin-solutions 1
• Remove sensor immediately if severe skin reaction occurs 1

Calibration and Accuracy Requirements

For CGM systems requiring calibration, perform fingerstick blood glucose measurements according to manufacturer specifications (typically 2-4 times daily) using FDA-approved meters with proven accuracy. 1

• Calibrate only when glucose is stable (not rapidly rising or falling) 1
• Use unexpired test strips purchased from licensed pharmacies or distributors 1
• Always maintain access to blood glucose monitoring equipment as backup, even with factory-calibrated sensors. 1

When to Perform Confirmatory Blood Glucose Testing

Perform fingerstick blood glucose testing in the following situations, regardless of CGM type: 1

• When CGM indicates hypoglycemia (<70 mg/dL or <3.9 mmol/L) 1
• When symptoms do not match sensor readings 1
• Before making treatment decisions during rapid glucose changes 1
• When sensor readings are outside target range (63-140 mg/dL during pregnancy; 70-180 mg/dL otherwise) 1

Medication and Substance Interference

Review all medications and supplements regularly, as several substances cause falsely elevated CGM readings and require reliance on blood glucose monitoring during their use. 1

Critical interfering substances include:

• Hydroxyurea (causes temporary falsely high readings) 1
• Intravenous mannitol or sorbitol 1
• High-dose vitamin C (ascorbic acid) 1
• Acetaminophen (device-dependent) 1

Data Interpretation and Target Ranges

Review CGM data using standardized Ambulatory Glucose Profile (AGP) reports focusing on time-in-range metrics rather than individual glucose points. 1

Standard targets for non-pregnant adults: 1

• Time in range (70-180 mg/dL): >70%
• Time below range (<70 mg/dL): <4%
• Time below range (<54 mg/dL): <1%
• Time above range (>180 mg/dL): <25%
• Glucose variability (coefficient of variation): <36%

Device Failure and Backup Plan

Maintain blood glucose meter, test strips, lancets, and insulin delivery supplies (syringes or pens) at all times as backup for sensor failure. 1

• Sensor signal loss, compression artifacts, or device malfunction require immediate reversion to blood glucose monitoring 1
• Contact device manufacturer technical support for troubleshooting persistent issues 1
• Never make insulin dosing decisions based solely on CGM during suspected device malfunction 1

Ongoing Support and Follow-up

Schedule regular follow-up to review CGM data, assess technique, evaluate skin condition, and reinforce proper use. 1

• Download and review CGM data at each diabetes visit 1
• Assess continued ability to interpret data and respond appropriately 1
• Interruption of CGM access is associated with worsening glycemic outcomes; ensure continuous device availability through insurance coverage. 1

Special Populations

For pregnant patients using CGM: 1

• Tighter target ranges apply (63-140 mg/dL or 3.5-7.8 mmol/L) 1
• Perform confirmatory blood glucose testing for values outside pregnancy-specific targets 1
• Real-time CGM with alarms is preferred over intermittently scanned systems 1

Common Pitfalls to Avoid

• Do not rely on estimated HbA1c calculations from CGM as equivalent to laboratory HbA1c testing 1
• Avoid sensor placement over areas receiving oxygen therapy or at high altitude, which can affect glucose oxidase-based sensors 1
• Do not assume all CGM systems are approved for non-adjunctive use (insulin dosing without confirmation); verify device-specific FDA approval 1
• Never ignore persistent skin reactions; continued use despite dermatitis can lead to spreading allergic reactions 1