Dexcom G4 User Manual page 131

Table 1 is categorized within YSI reference value ranges. When you know your
blood glucose level (measured by YSI in the study), this table shows how likely
your CGM reading matches with your blood glucose level. For example when
your blood glucose level is less than 80 mg/dL (4.4 mmol/L), you can expect
your CGM reading to be within 20 mg/dL (1.1 mmol/L) of YSI values, i.e. 60 to
100 mg/dL (3.4-5.6 mmol/L), 83% of the time.
Accuracy
Accuracy between matched pairs was also estimated by calculating the percent
difference between the System reading and the YSI value. For example, if the
YSI value is 100 mg/dL (5.6 mmol/L) and the System 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 2.
Overall, the System reads, on average, 13.3% absolute different (Mean Absolute
Difference) than the reference values. 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. The mean percent difference overall is 2.9%, and the
median percent difference overall is 1.7%. This shows that the system is biased
slightly higher than compared to the YSI.
Dexcom G4 User's Guide | 131