Point-of-care International Normalised Ratios: UK NEQAS experience demonstrates necessity for proficiency testing of three different monitors

Abstract

External quality assessment (EQA) or proficiency testing is widely considered to be necessary for International Normalised Ratio (INR) determinations performed in conventional laboratory settings. There is increasing use of near-patient-test (NPT) or point-of-care (POC) INR devices and it is not known whether EQA is also necessary for these monitors. We report here on six years experience of proficiency testing for POC monitors used by health care professionals. Three devices were used by >10 centres who participated in the programme, the CoaguChek (CUC), the CUC-S and the TAS or Rapidpoint Coag. Not all users of the same type of monitor obtained the same INR result when analysing the same plasma sample. For the three monitors the CV of results in different centres was 11-14%. The variation between results in different centres could relate to inappropriately handled proficiency testing material, inaccuracies in the calibration of the system by the manufacturer or deterioration during transport/storage of the test strips. In each survey 10-11% of centres using POC monitors obtained INR results which were >15% different from those in other centres using the same monitors. For hospital laboratories using conventional INR techniques this figure was 12%. The relationship between INR results obtained by users of the Rapidpoint Coag or TAS monitor and results obtained by conventional techniques was not constant over the period of study. During one period INRs with TAS were 13.7% greater than with conventional methods. For the remaining three time periods results were similar. Our data suggest that the variation between INR results determined with three POC monitors show similar variation to that observed in hospital laboratories using conventional methods. Based on our data we recommend that users of these POC monitors participate regularly in an independent external proficiency testing programme.