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Abstract
Background
Oral anticoagulation with warfarin requires routine monitoring of prothrombin time to maintain the international normalized ratio (INR) within the appropriate therapeutic range. CoaguChek XS (Roche Diagnositic, Germany) is a portable coagulometer that measures the INR. We evaluated the precision and accuracy of CoaguCheck XS by comparing it with CA-1500 (Sysmex, Japan).
Methods
We analyzed the CV and the correlation of all INR results measured in 68 samples obtained from patients treated with warfarin and 10 samples from control subjects with no history of anticoagulant therapy with CoaguChek XS and CA-1500. We compared the turn-around time between two instruments and evaluated the differences between the results obtained with venous and capillary blood samples and those obtained with different lots of the test strip. We also evaluated the precision of the two instruments in 5 repeated tests with samples of normal and increased INR.
Results
Mean INR values of 5 repeated tests with the same samples were similar. The correlation of INR values between two instruments was excellent (r2=0.97, P=0.001), and the difference in the values between the two instruments was mostly within the 95% limit of agreement, but was shown to increase in direct proportion to INR values. The turn-around time of CoaguChek XS was shorter than that of CA-1500. The differences between venous and capillary blood and between different lots of the test trip were not significant (P>0.05).
References
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Fig. 2.
Bias plot shows most of the value of difference between two methods are within the 95% limit of agreement (between upper and lower chain line).
Table 1.
Comparison of PT results of samples with normal and increased INR by 5 repeated tests using two instruments
|
Normal INR sample |
Increased INR sample |
|||
|---|---|---|---|---|
| CoaguChek XS | CA-1500 | CoaguChek XS | CA-1500 | |
| Mean | 0.99 | 0.96 | 3.16 | 2.95 |
| SD | 0.03 | 0.01 | 0.08 | 0.02 |
| CV | 3.19 | 0.59 | 2.67 | 0.53 |
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