Point of care international normalised ratio testing in acute cardiac wards

Abstract

Currently there may be considerable delay before international normalised ratio (INR) results are available. Many patients wait for results to undergo cardiac catheterisation, cardio-version or discharge. Point of care (POC) INR technology may offer benefits to patients, health care staff and facilities. There are few studies reporting its efficacy and impact on cardiovascular disease in patients on warfarin therapy,and one that report POC INR use in patients converting from heparin. The aim of this study was to compare the accuracy of INR results from POC testing with INR laboratory testing for patients receiving warfarin in an acute care setting and included patients being converted from intravenous heparin. POC INR testing was done by the bedside nurse, using CoaguChek XS, for 50 cardiovascular patients receiving warfarin. Formal INR laboratory testing was planned within one hour of the POC testing being performed, 38% of paired tests were performed on patients also receiving heparin. Results were compared using Spearman rank correlation and Bland-Altman plots. Fifty patients were enrolled in the study. A total of 117 paired INR results were collected, 44 from patients also on heparin. Results were highly significantly correlated (r = 0.953, p < 0.0001). Bland-Altman plots demonstrate a close agreement between POC INR and laboratory INR results for patients receiving warfarin regardless of whether they were receiving heparin. The difference between the paired results showed a median bias of +0.2. The presence of diabetes significantly reduced the difference between paired tests. Bias significantly increased above an INR of 4.5. 97% of all values fell between 20% limits of agreement after accounting for a fixed bias of +0.2. Results indicate the potential use of POC INR testing for clinical decision making for patients receiving warfarin within an acute care setting. Clinical guidelines, to be tested within a larger population group, are being developed.