MARD Accuracy Metrics

What is MARD?

Mean Absolute Relative Difference (MARD) is the gold-standard metric for CGM accuracy. It's calculated as the average percentage difference between sensor readings and a reference blood glucose value.

Industry Standards

A MARD of <10% is the industry threshold for non-adjunctive use—meaning dosing insulin without fingerstick confirmation.

Leading Device Performance

• FreeStyle Libre 3: 7.9% MARD
• Dexcom G7: 8.2% MARD

Limitations of MARD

MARD has important limitations:

The Averaging Problem

MARD is an average that can obscure poor performance in specific ranges, particularly hypoglycemia.

The Denominator Effect

At low glucose values, the percentage errors become inflated. A 10 mg/dL difference at 70 mg/dL is a 14% error, while the same absolute difference at 200 mg/dL is only 5%.

Comprehensive Evaluation

Clinical evaluation also relies on:

• Consensus Error Grid Analysis: Zone A/B placement indicates clinical accuracy
• iCGM regulatory standards: FDA requirements for automated insulin delivery compatibility