| Overall MARD | 8.2% |
| Warm-up Period | 30 minutes |
| Sensor Wear | 10 days + 12-hr grace period |
| Calibration | Factory calibrated (optional user cal) |
| FDA Designation | iCGM |
| Insulin Dosing Approved | Yes |
Key Takeaways
- Dexcom G7 has an 8.2% MARD (Mean Absolute Relative Difference) β among the best in class
- Lower MARD = more accurate readings vs your actual blood glucose
- No fingerstick calibration required for most users
- Accuracy can vary by sensor placement, hydration, and glucose rate-of-change
- FDA-approved for insulin dosing decisions without confirmatory fingerstick
What Is MARD and Why Does It Matter?
MARD (Mean Absolute Relative Difference) is the gold-standard metric for CGM accuracy. It measures the average percentage difference between a CGM reading and a simultaneous laboratory blood glucose reference. A MARD of 8.2% means the Dexcom G7's readings are, on average, within 8.2% of your true blood glucose value.
For context: if your actual blood glucose is 150 mg/dL, an 8.2% MARD means the G7 typically reads between 138β162 mg/dL. At clinically meaningful levels, this accuracy is sufficient for insulin dosing β which is why the FDA granted the G7 an iCGM designation.
Dexcom G7 Accuracy Specs
| Metric | Value |
|---|---|
| Overall MARD | 8.2% |
| Warm-up period | 30 minutes |
| Sensor wear duration | 10 days + 12-hour grace period |
| Calibration required | Optional (factory calibrated) |
| FDA designation | iCGM (integrated CGM) |
| Approved for insulin dosing | Yes |
How G7 Compares to Other CGMs
| CGM Device | MARD |
|---|---|
| Dexcom G7 | 8.2% |
| Dexcom G6 | 9.0% |
| Abbott Libre 3 | 7.9% |
| Medtronic Guardian 4 | 8.7% |
The G7 represents a meaningful improvement over its predecessor the G6, while remaining competitive with the Libre 3. Importantly, Dexcom's clinical data spans a broader glucose range and includes more hypoglycemia data points.
Factors That Affect Real-World Accuracy
Compression Lows
Lying directly on your sensor (especially at night) restricts interstitial fluid flow, causing falsely low readings. Alternate sensor placement sites to minimize this.
Rate of Glucose Change
CGMs measure interstitial glucose, not blood glucose directly. During rapid rises or falls (>2 mg/dL/min), there is a natural lag of 5β10 minutes. The G7's algorithm accounts for this, but fingerstick confirmation is wise during fast swings.
Sensor Placement
The G7 is approved for the upper arm and abdomen. Upper arm placement tends to show slightly higher accuracy in most users. Avoid scar tissue, waistbands, and areas with high movement.
Hydration and Temperature
Dehydration can concentrate interstitial fluid, skewing readings. Extreme temperatures (below 40Β°F or above 104Β°F) also impact sensor enzyme activity.
When to Confirm with a Fingerstick
- Symptoms don't match your CGM reading
- Glucose is rapidly rising or falling (arrows showing 2+ mg/dL/min)
- During the first 24 hours of a new sensor
- Before making a large insulin correction dose
MDS Diabetes carries a full range of blood glucose meters and test strips for those confirmatory checks β ensuring you always have a reliable backup.
Maximizing Your G7 Accuracy
- Insert sensor at least 30 minutes before you need reliable readings
- Rotate sites every session to prevent tissue irritation
- Keep the transmitter area dry for the first hour post-insertion
- Enter optional calibrations if readings feel consistently off
- Use the Dexcom G7 app alerts to catch compression lows early