No abstract

Summary The new CoaguChek XS system is designed for use in patient self testing with a measuring range from 0.8 INR up to 8.0 INR, which has been calibrated against the mean INR of rTF/95 and ERM‐AD149. This study was performed to confirm the correct INR results received from two routinely manufactured lots of test strips when compared with the international reference preparations (IRP) rTF/95 and ERM‐AD149. At one study site capillary and noncitrated venous whole blood samples from 20 normal donors and 62 anticoagulated patients were applied to two test strip lots of the new system in duplicate. Additionally blood was collected in citrate tubes, processed to plasma, and PT results were obtained using rTF/95 and ERM‐AD149 by the manual tilt tube method. Method comparisons of the INR results of the CoaguChek XS system vs. the mean INR of the IRP demonstrated a mean relative bias of −0.02% to −0.4%, mean absolute relative deviations of 6.4–9.6%, and accuracy observing >95% of CoaguChek XS INR within limits of ±14% to ±21.5% to the mean INR of the IRP. The results of the study confirm the successful calibration of two lots of the new CoaguChek XS system, demonstrate the validity of the calibration concept and prove the accuracy of the new system in comparison with the IRP. Clinical decisions in oral anticoagulation therapy may be reliably made upon the INR results of the new system.

The new CoaguChek XS system is designed for use in patient selftesting. It is the successor of the current CoaguChek S system. The detection principle is based on the amperometric measurement of the thrombin activity initiated by starting the coagulation cascade using a human recombinant thromboplastin. This study was performed to assign the International SEnsitivity Index (ISI) to the new test according to the WHO guidelines for thromboplastins and plasmas used to control anticoagulant therapy, and to establish the measuring range of the new system. At four study sites a total of 90 samples of normal donors and 291 samples of warfarin-, phenprocoumon- or acenocoumarol-treated patients were included in the study. The ISI value of the new test was assigned against the human recombinant reference thromboplastin rTF/95 at each site using the samples from stabilized patients in the International Normalized Ratio (INR) range between 1.5 and 4.5 only. The new point-of-care system's measuring range between 0.8 and 8 INR was calibrated against the mean INR of rTF/95 and AD149 using polynomial regression. ISIs were (CV of the slope): Site 1: ISI 0.99 (1.1%); Site 2: ISI 1.02 (2.0%); Site 3: ISI 1.03 (1.1%); Site 4: ISI 1.00 (1.4%). All regression lines calculated from patient-only data pass through the normal donor data points. All CVs of the slopes of the orthogonal regression lines are well below 3%, thus fulfilling the requirements of the WHO guidelines. The mean ISI for the new CoaguChek XS PT Test is 1.01.