Rev. Date: 05-Aug-11 Art: 716661-00F TCO2 - 3
Precision Data (mmol/L)
Aqueous Control Mean SD %CV
Level 1 17.4 0.62 3.6
Level 3 34.6 0.62 1.8
Method Comparison (mmol/L)
TCO
2
(Calculated)
IL BGE
TCO
2
(Calculated)
Beckman Coulter
CX
®
3
TCO
2
(Measured)
Beckman Coulter
LX
®
20
n 62 51 35
Sxx 0.40 0.55 0.48
Syy 0.84 0.55 0.60
Slope 1.136 1.155 1.152
Int’t -4.1 -2.6 -1.5
Sy.x 1.38 1.56 0.96
Xmin 19.3 18.3 21
Xmax 43.9 36.1 35
r 0.965 0.935 0.943
Cartridge Comparison
Performance characteristics for TCO
2
are equivalent in all cartridge configurations. System difference
analysis was performed on 40 patient samples using the i-STAT CHEM8+ and i-STAT EC8+ cartridges. In
the 14-30 mmol/L range, the average difference was -0.7 mmol/L.
Factors Affecting Results*
Exposing the sample to air allows CO
2
to escape which causes TCO
2
to be under-estimated. The use of
partial draw tubes (evacuated tubes that are adjusted to draw less than the tube volume, e.g. a 5 mL tube
with enough vacuum to draw only 3 mL) is not recommended for use with the i-STAT System because of the
potential for decreased TCO
2
values. Under-filling blood collection tubes may also cause decreased TCO
2
results. Care must also be taken to eliminate “bubbling” of the sample with a pipette when filling a cartridge
to avoid the loss of CO
2
in the blood.
Allowing blood samples to stand (without exposure to air) before testing allows TCO
2
to be over-estimated,
due to metabolic processes.
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