[Methodology and practical use in hemodialysis of the percentage of urea reduction (PUR)]

The determination of the perdialytic urea reduction ratio (URR) allows the quantification of the dialysis dosage actually delivered to patients. We studied the influence of the timing of the post-dialysis blood sampling on the URR, the reproducibility of URR and the practical steps to be taken to improve our patients' URR. URR (n = 31) is higher when blood sampling is performed before (62.4 +/- 4%) than after restitution of the blood circuit, either at the arterial (61 +/- 4.2%, p < .0001) or venous needle (60.7 +/- 4.2%, p < .50). Once blood sampling modalities are standardized in clinically stable patients with unchanged dialysis technique, URR proves highly reproducible (variation coefficient 2.4 +/- 1.2% of URR). To improve URR in 29 patients, blood flow (n = 20) and/or dialyzer surface (n = 14) were increased. In 3 patients HD session duration was increased. Altogether, the mean URR in these 29 patients rises from 57.1 +/- 3.8% to 63.4 +/- 4.3% (p < .0001). In conclusion, URR is influenced by the modalities of post-dialysis blood sampling. URR is reproducible in clinically stable patients with unchanged dialysis technique. URR was significantly improved in our patients by adaptations of HD technique (mainly blood flow and dialyzer surface).