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ePaper created 2014-10-06, 13:17:01 | version 1.33.00
been studied in a large population. A recent Health Technology Assessment (HTA) report in the UK noted that CoaguChek XS and INRatio2 had similar performance and their measurements correlated well with standard laboratory tests for INR [37]. However, this report also suggested that small differences in design or usability could have an impact on outcomes such as TTR or clinical events. Azarnoush et al. [38] did not find statistically significant differences for the clinical outcomes of 50 patients with mechanical valves using CoaguChek versus 40 patients using INRatio. Similarly Hemkens et al. [39] found that ‘‘the absolute and relative differences were not substantially different between both devices’’ in a study of 62 patients using INRatio and 65 patients using CoaguChek S for self-monitoring for any indication of VKA-therapy. In contrast to these small clinical trials, in this retrospective analysis results of more than 4,000 patients managed by the NTS using CoaguChek XS and INRatio2 with the same clinical protocol are reported. The current analysis adds to this understanding regarding the differences between the two monitors on both surrogate outcome parameters and clinical endpoints. While in the univariate comparison CoaguChek XS shows a statistically non- significant advantage of 1.1%, correcting for all identified influencers on the TTR such as gender, age, indications, medication, and target range still resulted in only a 1.0% difference in TTR, which was statistically significant. However, there was no difference in the distribution of minor clinical events that were self-reported by patients and the effect of the minor clinical events of the two monitors was not statistically significant and varied between the monitors. More importantly, there was no statistically significant influence of the monitor type on mortality. Hence, the current evidence suggests that there is no clinically relevant difference on clinical events between these two monitors. One of the key questions to be addressed is whether a 1.0% difference in TTR is relevant on outcomes other than clinical events. In accordance with others, this small difference was not considered to be practically relevant. Supporting this hypothesis, Rose et al. [35] showed in their model for a population of 67,077 patients based on a comprehensive meta-analysis that even TTR changes of 2.5% did not statistically significantly influence major clinical events like ischemic strokes or major hemorrhages, while impacting the death rate only marginally. Only at a 5% TTR change was there a significant influence on major clinical events. Similarly, Lam and colleagues [40] concluded that a TTR difference of 3.5% is not clinically relevant. The 1.0% difference observed between users of the two different monitors in the population of the NTS is well below these comparable TTR changes. Furthermore, the difference in TTR of the observed magnitude did not result in a notable difference between the incidences of minor clinical events. The CoaguChek XS showed a slight difference in two types of clinical event in multivariate statistical testing; however, this is deemed not to be clinically relevant and more likely due to the multiple tests performed in the large population analyzed. Most importantly, fatal events were not shown to be affected by the choice of the monitor in this analysis of over 4,000 patients. Strengths and Limitations The key strength of this retrospective analysis is the large population of more than 4,000 patients included, to our knowledge the largest consecutive cohort of self-monitoring Adv Ther