Comparison of Sampling Methods for International Normalized Ratio Monitoring in Haemodialysis Patients (INRHaemo...

Haemorrhagic and thrombotic complications are common in dialysis patients on warfarin; thus, accurate international normalized ratio (INR) monitoring is critical. For expediency and patient comfort, blood sampling from the haemodialysis access or circuit is commonly performed. Point-of-care (POC) INR machines allow both peripheral vein preservation and rapid results, yet are not validated in the haemodialysis population.

A prospective cohort study in haemodialysis patients taking warfarin was undertaken. Three paired samples were drawn over a single session: peripheral blood INR, POC INR, and dialysis INR. Agreement using Bland-Altman analysis and correlation coefficients between the peripheral blood INR, haemodialysis INR, and POC INR were calculated. Inappropriate dosing decisions based on haemodialysis or POC INR were quantified.

Amongst 34 patients, agreement between the dialysis INR and peripheral blood INR was high, with the haemodialysis INR differing from the peripheral INR by <±0.2, 85.2% of the time. Correlation between the 2 methods was high (r = 0.914; p < 0.001). POC INR differed from peripheral INR values by <±0.2, 67.6% of the time, with less agreement at higher INR values. Dosing decisions were incongruent between the dialysis and peripheral INR in 6%, whilst the POC and peripheral INR disagreed in 26%.

There was good agreement and correlation between the peripheral blood, haemodialysis access/circuit, and POC INR values. POC INR was less reliable at higher values, and dosing decisions differed from the peripheral INR in a quarter of cases.