User`s guide

130 | Dexcom G4 Continuous Glucose Monitoring System
11
System readings agreed with laboratory standard blood glucose results. The
remainder of the study took place at home, the System performance was also
paired with the comparative Lifescan OneTouch Ultra2 meter results, and that
is referred to as the ‘SMBG’.
Agreement
Agreement between the System and blood glucose values is characterized
using paired System and YSI values. The System and YSI results were
compared by pairing the YSI blood glucose value to a System glucose reading
that occurred immediately after the YSI was collected.
The agreement of the System to blood glucose value was assessed by
calculating the percentage of System readings that were within 20%, 30%,
and greater than 40% of the YSI values. For readings less than or equal to 80
mg/dL (4.4 mmol/L) the absolute difference in mg/dL (mmol/L) between the two
glucose results was calculated. For values greater than 80 mg/dL (4.4 mmol/L)
the absolute percent difference (%) from the YSI values was calculated. The
percentages of total readings within 20 mg/dL (1.1 mmol/L) or 20%, 30 mg/dL
(1.6 mmol/L) or 30%, or greater than 40 mg/dL (2.2 mmol/L) or 40% were then
calculated in Table 1.
The total number of data pairs considered in this analysis was 1477. Of these,
eighty percent (80%) of the System readings fall within ±20 mg/dL (1.1 mmol/L)
of the YSI blood glucose values (<80 mg/dL, i.e. 4.4 mmol/L) and within ±20%
of YSI blood glucose values (≥ 80 mg/dL, i.e. 4.4 mmol/L).
Table 1. Percentage of CGM System Readings within YSI Laboratory Values
Glucose Range
mg/dL (mmol/L)
Number of
YSI-CGM
Readings
Percent
within 20%
of YSI*
Percent within
30% of YSI*
Greater
than 40%
of YSI*
40-400 (2.2-22.2) 1477 80% 94% 2%
*For YSI less than 80 mg/dL (4.4 mmol/L), the absolute difference is presented as the
difference between the System and YSI, rather than the percent.
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 Laboratory
machine is reported. The System and YSI values were compared by pairing the
System reading that fell immediately after the YSI value was collected.