Here is some information from the Dexcom G5 Safety
Post# of 11802
Below copied in part from DEXCOM G5 Safety Information - website
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Important User Information
If your glucose alerts and readings from your Dexcom G5 do not match your symptoms or expectations, use a fingerstick blood glucose value from your blood glucose meter to make diabetes treatment decisions.
Diabetes Treatment Decisions
If your Dexcom G5 does not display a sensor glucose reading and an arrow or if you are getting inaccurate or inconsistent readings, use a fingerstick blood glucose value from your blood glucose meter to make diabetes treatment decisions.
Do Not Ignore Low/High Symptoms
Do not ignore symptoms of low or high glucose. If your glucose alerts and readings do not match your symptoms or expectations, y ou should obtain a fingerstick blood glucose value from your blood glucose meter to make diabetes treatment decisions or seek immediate medical attention.
Calibrate on Schedule
Calibrate the Dexcom G5 at least once every 12 hours. The Dexcom G5 needs to be calibrated in order to provide accurate readings. Do not use the Dexcom G5 for diabetes treatment decisions unless you have followed the prompts from the device and calibrated every 12 hours after the initial calibration.