User guide

The percentage of Guardian RT readings within 20 percent and 30 percent of YSI readings was analyzed
according to time after sensor insertion and according to the glucose-concentration range (as determined
by the YSI analyzer). See the following table.
Percentage of Guardian RT values
within 20% of YSI laboratory readings
Percentage of Guardian RT values
within 30% of YSI laboratory readings
Glucose Range
(mg/dl)
During first 60
hours of sensor
wear
After 60 hours of
sensor wear
During first 60
hours of sensor
wear
After 60 hours of
sensor wear
40-80
a
62-82% 39% 62-82% 39%
81-120 57-66% 48% 72-84% 66%
a. Agreement to within ± 20 mg/dL (1.1 mmol/L) for glucose readings ≤ 80 mg/dL (4.4 mmol/L)
Performance of the Guardian RT was evaluated according to the length of time since calibration. This data
is not conclusive because of the limited number of data points during the final 3 hours of the 12-hour
calibration cycle, i.e., 10. In contrast, 3-hour time bins, earlier in the 12-hour cycle, contained hundreds
of data points. This may suggest that calibrations are often required prior to the 12-hour calibration cycle.
Effects of calibration frequency
The average bias when Guardian RT was calibrated ~ 3.5 times a day was -20.5 ± 41 mg/dl (LL: -22.40
mg/dl and UL: -18.63 mg/dl). In those calibrated ~ 5 times a day, the bias was -10.2 mg/dl ± 36 mg/dl (LL:
-11.74 mg/dl and UL: -8.66 mg/dl). When comparing Guardian RT units that were calibrated less often to
those calibrated more often, the following alarm performance was observed:
• Specificity increased 2-4 percent in the hypoglycemic range and decreased 0-2 percent in the
hyperglycemic range
• Sensitivity increased between 5-9 percent across the hyperglycemic range, and decreased 7-16
percent when the alarm was set to 80 mg/dl or below, and decreased 3-7 percent when set between
85 and 100 mg/dl
Stratified error grid analysis also shows better performance in the hypoglycemic range when fewer
calibrations are performed, i.e., 62 percent of data points are in Zone A when fewer calibrations were
performed, whereas 58 percent were in Zone A when more calibrations were performed.
Appendix A144