Accuracy and reproducibility of urea recirculation in detecting haemodialysis access stenosis

Background: There is wide disagreement among studiesthat have evaluated the accuracy of urea recirculation (UR) in detectingvascular access stenosis. The 3-site method (UR3) has been discredited andreplaced by the 2-site method (UR2), but few studies have evaluated UR2.Methods: We compared the accuracies of UR2 and UR3 indetecting stenosis in 59 haemodialysis patients during a 12-month period.All patients were studied without regard to clinical suspicion of stenosis.Stenosis (⩾50% luminal narrowing) was diagnosed by duplexultrasound and confirmed by angiography. The reproducibility of UR2 wasdetermined by computing its total standard deviation (SDTOT) frommeasurements during three dialysis sessions over a 15-day period.Results: Stenosis was found in 32% of 124 accessstudies (mean luminal narrowing=58%, range=50-83%). The mean UR values ofstenotic accesses were only slightly higher than nonstenotic accesses forboth UR2 (7.6% vs 2.9%, P <0.01) and UR3 (13.1%vs 11.2%, P=0.22). An increase in blood pump speedfrom 300 to 425 ml/min did not improve detection of stenosis by UR2. Therewere no UR thresholds that cold adequately separate the presence ofstenosis from its absence. The SDTOT of UR2 was 3.8%, indicating that apatient's UR2 measurement may vary over a range of 16%(±2SDTOT=±8%). Conclusion:Stenosis of the haemodialysis access does not predictably causerecirculation, and the reproducibility of the UR2 measurement is poor.