Acceptability of CoaguChek S and CoaguChek XS generated international normalised ratios against a laboratory standard in a paediatric setting

Aims: Point of care (POC) testing is convenient for both patients and physicians but the accuracy of the results must be guaranteed. In this study we evaluated the accuracy of the international normalised ratios (INR) generated from the CoaguChek S and the newer CoaguChek XS against our laboratory standard. Methods: The INR values obtained from 87 tests on the CoaguChek S and 97 tests on the CoaguChek XS were compared with those generated from a laboratory based coagulation analyser. The results were statistically analysed. Results: The values from the CoaguChek XS were closer to the laboratory based results than those from the CoaguChek S but were still significantly different (p<0.001). Using an arbitrary INR difference of <= 0.5 INR units as a basis for comparable results, then 43% of the CoaguChek S and 19% of the CoaguChek XS results would have been considered unacceptable. Warfarin dose changes would have been considered in 25% of the CoaguChek S cases and 13% of the CoaguChek XS cases. Despite the disparity between the INR results from each of the methods, external quality assurance programs gave excellent results for both the CoaguChek S and the laboratory based INR results. Conclusions: The CoaguChek S INR will be within 0.5 INR units of the laboratory result up to an INR of 4 in only 66% of cases compared with 96% for the CoaguChek XS. Thus this study suggests that CoaguChek S machines should be substituted with CoaguChek XS and these can be used with confidence for INR results up to 4.