T RAJKUMAR1, L WEIDERSEHN2, L SURMON1, M HARVEY3, J WONG2, A MAKRIS2
1Department of Medicine, Campbelltown Hospital, SWSLHD, Campbelltown, Australia, 2Renal department, Liverpool Hospital, SWSLHD, Liverpool, Australia, 3Haematology Department, Liverpool Hospital, SWSLHD, Liverpool, Australia
Aim: To compare international normalised ratio (INR) monitoring using haemodialysis access/circuit blood samples or a point-of-care INR (POC-INR) device, to the gold-standard peripheral blood INR (pINR) in maintenance haemodialysis patients taking warfarin.
Background: Haemorrhagic and thrombotic complications are common in dialysis patients on warfarin, thus accurate and reproducible INR monitoring is critical. For expediency, patient comfort, and vein preservation; blood sampling from the haemodialysis access or circuit is commonly performed at many institutions. POC INR machines allow both peripheral vein preservation and rapid results, yet are not validated in the haemodialysis population.
Methods: A multi-site prospective cohort study in maintenance haemodialysis patients taking warfarin was undertaken. Three samples were drawn over a single session: pINR, POC-INR (Roche© CoaguChek) and dialysis INR (nurse blinded, as per routine practice). Paired comparisons were undertaken to assess correlation between pINR and dialysis INR (primary outcome) and between pINR and POC-INR (secondary outcome). Inappropriate dosing decisions based on dialysis or POC-INR were quantified. Analysis was undertaken with SPSS.
Results: Amongst 34 patients, correlation between the dialysis INR and pINR was r=0.914;p<0.001. Dialysis INR differed with pINR by less than ±0.2 85.2% of the time. Correlation between pINR and POC INR was r=0.950;p<0.001. POC-INR differed with pINR values by less than ±0.2 INR 67.6% of the time, with less agreement at higher INR values. Dosing decisions were incongruent between the dialysis INR and pINR in 2(6%) instances, whilst the POC-INR and peripheral INR disagreed in 8(26%) instances.
Conclusions: There was good agreement between the pINR, haemodialysis access/circuit and POC-INR values. Dosing decisions were minimally affected using the dialysis INR, but reliance on POC-INR would affect a quarter of dosing decisions.
Theepika Rajkumar is currently an Obstetric Medicine fellow in South Western Sydney, having completed her Nephrology training in 2019.