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

Am J Nephrol. 2021;52(1):17-25. doi: 10.1159/000513094. Epub 2021 Feb 8.


Background: 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.

Methods: 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.

Results: 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%.

Conclusions: 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.

Keywords: Haemodialysis; International normalized ratio; Point-of-care; Sampling; Warfarin.

Publication types

  • Comparative Study

MeSH terms

  • Aged
  • Aged, 80 and over
  • Anticoagulants / therapeutic use*
  • Blood Specimen Collection / methods*
  • Female
  • Humans
  • International Normalized Ratio*
  • Kidney Failure, Chronic / blood*
  • Kidney Failure, Chronic / therapy*
  • Male
  • Middle Aged
  • Prospective Studies
  • Renal Dialysis*
  • Warfarin / therapeutic use*


  • Anticoagulants
  • Warfarin