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True Threshold Hypoglycemic alert rate alerted when the CGM system read that
the user was below the low threshold and the user’s BG was actually below that
low threshold.
True Threshold Hyperglycemic alert rate alerted when the CGM system read that
the user was above the high threshold and the user’s BG was actually above that
high threshold.
True Predictive Hypoglycemic alert rate alerted when the CGM system predicted
that the user would reach below the low threshold and the user’s BG was actually
below that low threshold within 15 or 30 minutes.
True Predictive Hyperglycemic alert rate alerted when the CGM system predicted
that the user would reach above the high threshold and the user’s BG was actually
above that high threshold within 15 or 30 minutes.
The true alert rate is important because it is necessary that users be notified when
their BG is low (or high) so that they can correct the low (or high) BG. A high true
alert rate indicates that when the CGM system says that their glucose values are, or
will reach a specified threshold, the user’s BG is likely to be at or approaching that
threshold.
For example, per the following table, when wearing the sensor in the abdomen,
the low glucose alerts would have correctly indicated that the user was below (i.e.
threshold only), or predicted to reach below the threshold (i.e. predictive only), or
both (predictive and threshold) 44.4%, 28.6%, or 36.4% of the time within 30
minutes (or 44.4%, 14.3%, or 27.3% of the time within 15 minutes) when the user
had BG values lower than 70 mg/dL.
Table F-1: Glucose TRUE Alert Performance using Calibration every 12 hours
Glucose TRUE Alert Rate
mg/dL Insertion Site Threshold Only Predictive Only Threshold & Predictive
30 min 15 min 30 min 15 min 30 min 15 min
50 Abdomen 33.3% 33.3% 12.5% 12.5% 18.2% 18.2%
Buttock 25.0% 25.0% 11.1% 11.1% 16.7% 16.7%
60 Abdomen 25.0% 25.0% 8.3% 8.3% 12.5% 12.5%
Buttock 60.0% 60.0% 25.0% 16.7% 35.3% 29.4%
70 Abdomen 44.4% 44.4% 28.6% 14.3% 36.4% 27.3%
Buttock 60.0% 60.0% 36.8% 26.3% 40.7% 33.3%
80 Abdomen 33.3% 33.3% 31.6% 15.8% 32.3% 22.6%
Buttock 61.1% 61.1% 46.2% 38.5% 51.2% 46.5%
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