NDT Advance Access originally published online on January 23, 2008
Nephrology Dialysis Transplantation 2008 23(5):1772-1773; doi:10.1093/ndt/gfm905
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The effect of sodium citrate 4% locking solution for central venous dialysis catheter on the international normalized ratio (INR) value
Correspondence and offprint requests to: E-mail: jp{at}complices.qc.caSir,
We read with great interest the article by Grudzinski et al. [1], demonstrating the benefits of sodium citrate 4% locking solution for central venous catheters. The authors concluded that citrate locking improves reliability of international normalized ratio (INR) measurement compared to standard heparin locking. Unfortunately, the study was not designed specifically to assess this question. In addition, the authors reported a surprisingly low incidence (0.8%) of falsely elevated INR due to heparin contamination following heparin locking. They also reported an absence of falsely elevated INR following citrate locking. Such findings are unexpected, given that INR may be clearly overestimated when the blood is contaminated with either heparin [2] or citrate [3–5].
We performed a pilot study with 19 haemodialysis (HD) patients at our centre to assess the reliability of INR measurement when blood samples are drawn directly from central catheters locked with either sodium citrate 4% or standard heparin. INRs were measured simultaneously prior to dialysis from both a peripheral vein and the HD catheter after discarding 5 cc of blood from the arterial port. The INR values obtained following citrate or heparin locking were compared using ANOVA.
We found that INR values were falsely elevated in all patients with heparin lock. The mean INR was falsely elevated by 56% ± 28% (INR catheter: 1.7 ± 0.3; INR peripheral vein: 1.1 ± 0.04) in patients without warfarin (n = 7), whereas the mean INR was overestimated by 114% ± 51% (INR catheter: 4.8 ± 1.4; INR peripheral vein: 2.1 ± 0.15) in patients with warfarin (n = 12). In contrast, INRs drawn from citrate-locked catheters were not or were only minimally elevated compared to samples drawn from peripheral venipuncture. In patients without warfarin, the mean INR was increased by 0.04% ± 0.7% (INR catheter: 1.06 ± 0.02; INR peripheral vein: 1.06 ± 0.03) whereas in patients with warfarin, the mean INR was increased by 1.9% ± 0.6% (INR catheter: 2.20 ± 0.16; INR peripheral vein: 2.19 ± 0.16).
These results clearly demonstrate that sodium citrate catheter locking minimally interferes with INR measurements when blood is drawn directly from the catheter prior to dialysis treatment. They also demonstrate that the overestimation of INR with heparin locking is more frequent than reported by Grudzinski et al. [1]. Hence, the use of citrate catheter locking improves INR measurement reliability and thus facilitates the management of anticoagulation in HD patients.
Conflict of interest statement. None declared.
Nephrology Division, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada
References
- Grudzinski L, Quinan P, Kwok S, et al. Sodium citrate 4% locking solution for central venous dialysis catheters—an effective, more cost-efficient alternative to heparin. Nephrol Dial Transplant (2007) 22:471–476.
[Abstract/Free Full Text] - Leech BF, Carter CJ. Falsely elevated INR results due to the sensitivity of a thromboplastin reagent to heparin. Am J Clin Pathol (1998) 109:764–768.[Web of Science][Medline]
- Chantarangkul V, Tripodi A, Clerici M, et al. Assessment of the influence of citrate concentration on the international normalized ratio (INR) determined with twelve reagent- instrument combinations. Thromb Haemost (1998) 80:258–262.[Web of Science][Medline]
- Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol (1997) 107:105–110.[Web of Science][Medline]
- Duncan EM, Casey CR, Duncan BM, et al. Effect of concentration of trisodium citrate anticoagulant on calculation of the international normalised ratio and the international sensitivity index of thromboplastin. Thromb Haemost (1994) 72:84–88.[Web of Science][Medline]
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