European Concerted Action on Anticoagulation (ECAA). Minimum number of centres for reliable international sensitivity index calibration of CoaguChek and TAS point-of-care whole blood monitors

Introduction: Prothrombin time (PT) test systems require multicentre calibration for reliable International Sensitivity Index (ISI). Multicentre calibration of CoaguChek Mini and TAS PT-NC point-of-care test (POCT) systems is less precise than conventional PT testing. The aim of the present study was to determine the number of centres required to give reliable ISI and International Normalised Ratio (INR) with these two POCT whole blood PT monitors. Materials and methods: A simulation study, based on results of a 10-centre calibration exercise, was performed to assess reliability of ISI and INR when the number of centres was reduced from 10 to 2. Results and Conclusions: With both systems, the range of ISI and INR deviation increased as the number of centres was reduced. For the CoaguChek Mini, at least five centres were needed for satisfactory INR deviation in 95% of calibrations. With the TAS PT-NC, three centres gave satisfactory INR at this level. The number of centres required for multicentre calibration of these two POCT PT systems is greater than the two proposed by World Health Organisation (WHO) Guidelines for conventional PT testing.