User`s guide

190 | Dexcom G4 PLATINUM Professional Continuous Glucose Monitoring System
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readingis90mg/dL(5.0mmol/L),a10%differencebetweentheSystem
and the YSI is reported. The System and YSI values were compared by
pairing the System reading that fell immediately after the YSI value was
collected.
In the example above the System reading is less than the YSI value, so
the percent difference reading is negative. The mean percent difference
is the average of all positive and negative percent differences between
the two devices; it tells you if the System reads higher or lower on
average than the YSI at each glucose range.
Another estimate used to show the accuracy of the System is the
absolute percent difference. The absolute percent difference tells you
the percent difference or “distance” between the System and YSI values,
but does not tell you whether the System is reading, on average, higher
or lower than the YSI laboratory standard. The mean absolute percent
difference is the average “distance” (regardless if positive or negative)
between System readings and YSI values.
These accuracy measures in differences are based on 9152 paired
glucose results and summarized in the following Table 4-A and Table
4-B.
Overall,theSystemreads,onaverage,2.9%different(MeanPercent
Difference)thanthereferenceand13.3%absolutedifferent(Mean
Absolute Difference) than the reference values. The Median Percent
DifferenceshowsthathalfofthetimetheSystemreads1.7%orless
than the YSI blood glucose values and the Median Absolute Percent
DifferenceshowsthathalfofthetimetheSystemreadsabout9.8%or
less different than YSI blood glucose values.