Transcript VRE

COMPARISON OF THE RADIOMETER AQT 90 FLEX ANALYSER VERSUS
BECKMAN COULTER DxI 800 FOR THE MEASUREMENT OF TROPONIN I.
L MACKAY, N CRINIS, Q LAM, R SCOTT
Biochemistry Department, Austin Pathology, Austin Health, Heidelberg Vic. 3084, Australia
[email protected]
Correlation by linear regression yielded the equation:
METHOD
Evaluation of the AQT90 Flex TnI was performed within the laboratory.
Analytical precision was evaluated using a low positive patient serum
pool and two levels of a commercially available quality control material
(Bio-Rad).
For the correlation study, 165 EDTA plasma patient samples with a
corresponding serum/lithium heparin plasma TnI ≥ 0.01 ug/L on the
Beckman Coulter AccuTnI (Unicel DxI 800) were selected. All EDTA
samples were analysed within four hours of collection on the AQT90
Flex. Statistical analysis was performed using a commercial statistics
program (Analyse-it, version 2.09)
DxI = 4.394AQT – 0.105, (R2 = 0.90)
across a DxI range of 0.02ug/L to 57.84 ug/L. See Figure 2a.
Using the respective 99th percentile cut-off for each assay, 121/165
paired samples agreed in interpretation (i.e. elevated or negative by
both assays).
44 did not agree (see Figure 2b). All 44 were above the DxI cut-off but
not the AQT. It was beyond the scope of this evaluation to determine
which assay performed better clinically. However, it is important to note
that the assays are not traceable to a common calibrator source and
that the respective cut-offs were determined on different reference
populations and hence not directly comparable. Furthermore, Beckman
Coulter has since re-formulated the AccuTnI to improve performance at
the low end.
Correlation using paired patient samples.
Correlation using paired patient samples - low
values
60
0.2
50
0.18
0.16
40
Beckman AccuTnI (ug/L)
Troponin I (TnI) is the biochemical marker of choice for assessing
patients presenting to the Emergency Department with cardiac
symptoms. Given the urgent nature of such requests, a rapid turnaround-time (TAT) is an important prerequisite for troponin assays and
one which makes point-of-care testing attractive to clinicians.
We evaluated the performance of the TnI assay on the Radiometer
AQT90 Flex analyser to determine its suitability as a point of care
option for our tertiary hospital Emergency Department.
Beckman AccuTnI (ug/L)
INTRODUCTION
30
20
10
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
RESULTS & DISCUSSION
Sample type
Minimum volume
Analysis Time
99th % ref pop.
Calibrator
traceability
5
Linear fit (-0.105 +4.394x)
Figure 1 highlights characteristics of both TnI assays. Although analysis
time is lower with the AccuTnI assay, sample transportation to the
laboratory and sample preparation adds to overall TAT of the AccuTnI
result.
AQT
0
DxI
Plasma
(Lithium Hep/EDTA)
Serum /Plasma
(Lith Hep/EDTA)
2ml
18 min
0.023 ug/L
200uL
13 min
0.04 ug/L
NIST SRM 2921
EN ISO 17511
Figure 1. Assay characteristics of the AQT90 Flex TnI versus the AccuTnI
as described by the manufacturers.
The coefficient of variation (CV) for the patient pool (mean 0.043 ug/L)
was 11.2%. Using QC material, CV was 9.1% at a level of 0.42 ug/L and
11.9% at a level of 1.64 ug/L.
10
AQT TnI (ug/L)
95% CI
0
0.02
0.04
0.06
AQT TnI (ug/L)
Figure 2 a. Overall correlation between the AQT90 Flex TnI versus the AccuTnI.
b. Correlation at low TnI values with respective 99th % reference population cut-offs.
CONCLUSION
The results generated by the AQT90 Flex TnI assay are numerically
different to the AccuTnI DxI 800 assay but with the application of an
appropriate slope and intercept, the AQT90 Flex TnI assay can be
used in the Emergency Department setting to produce results
comparable to the laboratory assay. However, it is important that
clinicians are aware that the assays are fundamentally different.
REFERENCES
1. AQT90 Flex. TnI Test Kit package Insert. Radiometer 2008.
2. AccuTnI package insert Ref 33340. Beckman Coulter 2006.
ACKNOWLEDGEMENTS
We thank Radiometer for the supply of reagent and instrument for this study