Continuous Glucose Monitors (CGM): Clinical Comparison
A data-driven breakdown of the major RT-CGM (Real-Time) and isCGM (Intermittently Scanned) systems available on the market.
Core Metrics Comparison
Data sourced from primary FDA pre-market approval documents and published peer-reviewed studies (references below). MARD (Mean Absolute Relative Difference) is the standard metric for accuracy; lower is better.
| Device | Overall MARD | Wear Time | Warmup | Calibration | Size (Volume) |
|---|---|---|---|---|---|
| Dexcom G7 | 8.2% | 10 Days (+12hr grace) | 30 minutes | None required | ~60% smaller than G6 |
| FreeStyle Libre 3 | 7.9% | 14 Days | 60 minutes | Factory calibrated | Size of two stacked pennies |
| Dexcom G6 | 9.0% | 10 Days | 2 hours | None required | Requires separate transmitter |
| Medtronic Guardian 4 | 8.7% (with 780G) | 7 Days | 2 hours | None required | Rechargeable transmitter |
Algorithm Integrations (AID)
A CGM's utility is magnified when paired with an Automated Insulin Delivery (AID) system. Current official integrations:
- Dexcom G6: Tandem t:slim X2 (Control-IQ), Omnipod 5, Beta Bionics iLet
- Dexcom G7: Tandem t:slim X2 (recently approved), Beta Bionics iLet
- FreeStyle Libre 2/3: In development / partial rollout with Ypsomed and Omnipod 5 (Europe)
- Guardian 4: Medtronic 780G (SmartGuard)
Common Mistakes in CGM Analysis
1. Overweighting MARD differences under 1%: The difference between 7.9% and 8.2% MARD is statistically significant in trials, but clinically negligible for most individuals due to insertion site variables.
2. Ignoring Vitamin C interference: Older generation sensors (like Libre 14-day) show false highs with Ascorbic Acid. G6/G7 and Libre 2/3 have largely mitigated this, but limits exist (e.g., >1000mg/day for G6).
FAQ
Does paracetamol/acetaminophen affect readings?
Dexcom G6 and G7 resist acetaminophen interference up to 1,000mg every 6 hours. Older Medtronic sensors may still show interference.
Why do first-day readings seem inaccurate?
The insertion trauma causes a local inflammatory response, leading to fluid shifts in the interstitial tissue. Algorithms filter this "sensor noise," but Day 1 MARD is universally higher than Days 2-10 across all devices.