ACCURACY AND REPRODUCIBILITY OF UREA RECIRCULATION IN DETECTING HEMODIALYSIS ACCESS STENOSIS

Background. There is wide disagreement among studies that have evaluat ed the accuracy of urea recirculation (UR) in detecting vascular acces s stenosis. The 3-site method (UR3) has been discredited and replaced by the 2-site method (UR2), but few studies have evaluated UR2. Method s. We compared the accuracies of UR2, and UR3 in detecting stenosis in 59 haemodialysis patients during a 12-month period. All patients were studied without regard to clinical suspicion of stenosis. Stenosis (g reater than or equal to 50% luminal narrowing) was diagnosed by duplex ultrasound and confirmed by angiography. The reproducibility of UR2 w as determined by computing its total standard deviation (SDTOT) from m easurements during three dialysis sessions over a 15-day period. Resul ts. Stenosis was found in 32% of 124 access studies (mean luminal narr owing = 58%, range = 50%-83%). The mean UR values of stenotic accesses were only slightly higher than non-stenotic accesses for both UR2 (5. 6% vs 2.9%, P < 0.01) and UR3 (13.1% vs 11.2%, P = 0.22). An increase in blood pump speed from 300 to 425 ml:min did not improve detection o f stenosis by UR2. There were no UR thresholds that could adequately s eparate the presence of stenosis from its absence. The SDTOT of UR2 wa s 3.8%, indicating that a patient's UR2 measurement may vary over a ra nge of 16% (+/-2SD(TOT) = +/-8%). Conclusion. Stenosis of the haemodia lysis access does not predictably cause recirculation, and the reprodu cibility of the UR2 measurement is poor.