Abstract 18842: Point of Care Testing Overestimates INR in CF-LVAD Patients

Abstract

Background: Long-term anticoagulation therapy with warfarin is used in pts. with continuous-flow LVAD (CF-LVAD) to minimize the occurrence of thromboembolic events. Patient self-testing (PST) of INR with home monitoring devices has been shown to improve time within therapeutic INR range as well as patient satisfaction in other settings. However, PST devices have never been tested in pts. with CF-LVADs. The purpose of this study was to determine the reliability of PST devices in patients supported with CF-LVADs. Methods: A correlation study was performed in 50 CF-LVAD pts. who were on stable warfarin therapy for a minimum of 3 weeks. Simultaneous INR values were determined from capillary whole blood samples using the Alere home monitoring PST device and venous blood samples processed in the core laboratory at a large volume CF-LVAD center. Hematocrit, liver function tests, TSH, and amiodarone use were also recorded on patients due to their propensity to affect warfarin metabolism and INR results. Results: Fifty LVAD pts with a mean age of 60 (±14) years were included in the study. Forty-one (82%) were male, and the mean time on CF-LVAD support at the time of INR measurement was 12 months, ranging from 1 to 56 months. There was a moderate correlation between the venous and capillary INR values with a correlation coefficient of 0.83 (r 2 =0.68, p<0.001; Fig 1a). The median difference between the methods was 0.39, with 44/50 pts. having higher INRs with Alere (Fig 1b). Results remained the same after controlling for the use of amiodarone, abnormal hematocrit and liver enzymes, creatinine and TSH. Conclusion: Point of care testing with Alere consistently overestimates INR when compared to conventional laboratory testing in CF-LVAD patients. While our data requires large scale validation, similar results have been reported with point of care testing in other patient populations. Once validated, failure to adjust for this difference may lead to unintentional subterapeutic INR.