Clinical interpretation of the Uremic Pruritus in Dialysis Patients (UP-Dial) scale: a novel instrument for the assessment of uremic pruritus

Background The Uremic Pruritus in Dialysis Patients (UP-Dial) scale is valid and reliable for uremic pruritus (UP) assessment. However, it remains unknown how the scores should be interpreted in clinical practices. Objectives To establish a clinical interpretation of the UP-Dial by identifying severity cut-off scores according to the disease severity and burden of pruritus. Methods This cross-sectional study developed a classification system for the UP-Dial scores using the patient-based anchors method. From May 2012 through January 2017, 697 dialysis patients were screened. Of these, a total of 258 met the criteria for UP and completed the UP-Dial scale and three sets of patient-assessed anchor questions: (i) global UP intensity by visual analogue scale (VAS)-UP, (ii) Dermatology Life Quality Index and (iii) global kidney disease-related quality of life. The cut-off scores were generated based on the kappa (kappa) coefficient of agreement and the area under receiver operating characteristic curve (AuROC) statistics. Subgroup analyses were performed to explore associations between patient characteristics and the UP-Dial severity bands. Results The proposed scores were <= 12 (mild), 13-21 (moderate) and >= 22 (severe) with kappa coefficient ranging between 0.39 and 0.46. Assigned scores were associated with all patient-based anchors. The highest association was with the VAS-UP, and AuROC was 0.80 (mild; 95% CI, 0.75-0.86), 0.66 (moderate; 0.60-0.71) and 0.83 (severe; 0.77-0.89). In subgroup analysis according to patient characteristics, we did not find any significant difference. Conclusions The estimated UP-Dial severity band can facilitate the interpretation of UP in practice-based research settings and can be used to support treatment decisions.