Comparing Point of Care International Normalised Ratio testing with laboratory testing methods in a cardiac inpatient population

Aims and objective:  To compare agreement between International Normalised Ratio results from Point of Care testing with laboratory testing for cardiac inpatients receiving warfarin sodium. Background:  Availability of point of care technology for International Normalised Ratio testing offers considerable benefits to patients and health care staff across a range of context. Design: Prospective comparison study. Method:  Setting – Four cardiac wards in a regional referral hospital in New South Wales, Australia. Participants – 50 cardiovascular inpatients receiving warfarin therapy, including those patients being converted from intravenous heparin sodium. Intervention-Point of Care International Normalised Ratio testing via finger prick using the CoaguChek®XS attended within one hour of laboratory International Normalised Ratio testing. Paired International Normalised Ratio results were compared using spearman rank and Mann–Whitney rank sum. Bland–Altman plots were used to demonstrate agreement. Results: One hundred and seventeen blinded paired tests were carried out, 44 on patients receiving intravenous heparin. Laboratory and Point of Care International Normalised Ratio testing were highly significantly correlated (r = 0·953, p < 0·0001, n = 117). There was close agreement between Point of Care International Normalised Ratio and laboratory International Normalised Ratio results for patients receiving warfarin regardless of whether they were receiving heparin sodium. There was a mean bias of +0·2 units (95% CI 0·145–0·246). The presence of diabetes significantly reduced the difference between paired tests. Bias significantly increased above an International Normalised Ratio of 4·5 units. Ninety-seven per cent of all values fell between 20% limits of agreement after accounting for the mean bias of +0·2 units. Conclusion: Results indicated Point of Care International Normalised Ratio testing can be used for clinical decision making for cardiovascular inpatients receiving warfarin. Clinical guidelines need to be developed and tested in appropriate population groups and across different contexts, because of the potential for significant patient benefit.