Interesting accuracy numbers for a finger prick meter and Libre 3
For CGMs, accuracy is given in two forms:
(A) Percentage of matched glucose pairs within ±20mg/dL (or 20%) of reference values within glucose ranges, or
(B) MARD. ARD is the absolute percentage difference between the CGM value and the true blood glucose value at the same time point, whereas MARD is the average of many pairs of ARDs. It tells how accurate the CGM is when compared to the true blood glucose. It is mainly used to compare different brands of CGMs. Measurement of MARD is complex and has to specify the condition.
(A) is also given in ±40mg/dL (or 40%) and what is interesting is that the percentage is 100% that is with absolute certainty that is the case.
I am using Contour Next and interested in the range from 70-100 mg/dL because <70 is hypoglycemia and because I do not expect calibration will cover a range greater than 30 mg/dL.
Below is hand-waving in order to get a ball part number.
(A) Accuracy of Contour Next given by the manufacturer, ascensiadiabetes, is given in the above figure, which shows that when the BG is <100mg/dL, 100% of results is within ±10mg/dL
Accuracy of the Libre 3 is given in Table 3a (reproduced in above figure) of “Accuracy of a 15-day Factory-Calibrated Continuous Glucose Monitoring System With Improved Sensor Design”.
For the range of 70-100 mg/dL, “% Within ±40 mg/dL”, it is ~100% and the MARD is ~9% (I interpolate).
Thus, ratio of accuracy of Libre 3 to Contour One is ±40mg/dL/ ±10mg/dL= 4/1.
(B) MARD for the Contour One is given in Table 4 of “User Performance Evaluation and System Accuracy Assessment of Four Blood Glucose Monitoring Systems With Color Coding of Measurement Results” for 3 lots of test strips.
They are 2.3 ± 1.7, 2.4 ± 1.6, 2.3 ± 1.8.
Thus, MARD ratio of Libre 3 to Contour Next is ~9/2.3 = ~4. Approximately the same as the ratio in mg/dL.
Posted Jun 6, 2026, 3:14 PM UTC