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ePaper created 2014-10-06, 13:17:01 | version 1.33.00
Under VKA treatment, the quality of INR adjustment and the resulting TTR is strongly correlated with the outcome of patients in terms of thrombotic events and the rate of complications, particularly anticoagulant- induced bleeding. Regarding the quality of INR control, a high TTR of 87.9% was observed in the patients in this analysis. It should be noted that this analysis of Dutch patients used a therapeutic INR range of 2.0–3.5 for most of the patients, while internationally a target range of 2.0–3.0 is used for most indications for VKA anticoagulation. The corresponding time in target range for the NTS data is calculated at 68.9%, which bears close comparison to the recently published STABLE retrospective analysis of 24,907 warfarin- anticoagulated patients on INR self-testing, with an overall TTR of 69.7% [8]. It should be noted though that maintenance within this narrower range is not a priority for NTS. Comparison with TTR values reported from randomized clinical trials is difficult because of the differences in parameters measured, level of monitoring and pre-specified endpoints. Apart from TTR, the frequency of critical INR values is an important indicator for the quality of VKA anticoagulation; this aspect has even been regarded to be more suitable for the prediction of clinical events than the TTR. As with others, critical INR values were defined as those below 1.5, bearing a considerable risk for thrombotic or thromboembolic events, and those above 5.0, predisposing for bleeding complications [8, 19]. In our data, an average of 2.4% of the INR values per patient was within the critical range. The frequency of critical values observed in this study of an average of 0.085 per month compares slightly favorably to the overall average frequency of 0.096 per month implied in the STABLE population [8]. This is interesting since the two populations not only used different VKA (in the USA predominantly warfarin, which has a longer half-life than acenocoumarol but shorter than phenprocoumon), but in addition medical practice in the NTS population favoured the somewhat more aggressive treatment of atrial fibrillation to an INR target range of 2.5–3.5. This suggests that patient self-testing is able to achieve this more aggressive target in the Netherlands with the same quality of control, shown by the equivalent TTR. In general, the results indicate a high quality of INR control in the NTS population, indicated by both high TTR and low prevalence of critical INR values. This raises the question whether the good INR control resulted in an effective prevention of thrombotic and thromboembolic events on the one hand and the prevention of serious complications of treatment on the other. Taken together the self-testing population analyzed in the Netherlands compares very similarly in setup and therapy control to the populations studied elsewhere. This INR management system seems representative of a typical self-monitoring therapy with the associated beneficial effects on therapy control. The analysis demonstrates a good level of INR control and, consequently, high TTR in patients performing self-testing of INR. As shown, good INR control by self-testing also leads to high efficacy of treatment and high treatment safety, indicated particularly by an acceptable prevalence of minor bleeding complications and low death rate due to major clinical events under VKA treatment. A review of the literature on the analytical performance of point of care INR monitors, including CoaguChek XS and INRatio among others, concludes that in general they have adequate precision and accuracy for clinical use [36]. The effect of the choice of home monitor to measure INR has to our knowledge so far not Adv Ther