Psychometric evaluation of the multidimensional Uraemic Pruritus in Dialysis patients (UP-Dial) scale: comparison of haemodialysis and peritoneal dialysis patients with chronic pruritus

Abstract Background High-quality patient-reported outcome (PRO) measures for dialysis patients with chronic pruritus are urgently needed. However, no known, well-validated multidimensional tools have been investigated to measure pruritus symptoms in dialysis patients. Objectives To examine the psychometric properties of a multidimensional tool of chronic pruritus, the Uraemic Pruritus in Dialysis patients (UP-Dial) 14-item scale, by comparing haemodialysis and peritoneal dialysis modality. Methods This validation study used data from the Thai Renal Outcomes Research-Uraemic Pruritus, a prospective, multicentre, longitudinal study. Data for this study were collected from 1 February 2019 to 31 May 2022. The adult sample of 226 haemodialysis and 327 peritoneal dialysis patients fulfilled the criteria of chronic pruritus based on the International Forum for the Study of Itch. Psychometric properties of the UP-Dial included validity and reliability, as measured across haemodialysis and peritoneal dialysis patients. Patients completed a set of anchor-based measurement tools, including global itching, Dermatology Life Quality Index (DLQI), EuroQoL-5 dimension-5 level (EQ-5D-5L), Kidney Disease Quality of Life-36 (KDQOL-36), Pittsburgh Sleep Quality Index (PSQI), global fatigue, Somatic Symptom Scale-8 (SSS-8) and Patient Health Questionnaire-9 (PHQ-9). Results From the patient’s perspective, face validity was satisfactory for both dialysis samples. Psychometric analyses of the UP-Dial for each dialysis sample had good convergent validity. Spearman rho correlations indicate a positively strong correlation (0.73–0.74) with global itching, a positively moderate correlation (0.33–0.58) with DLQI, PSQI, global fatigue, SSS-8 and PHQ-9, and a negatively moderate correlation (–0.39 to –0.58) with EQ-5D-5L and KDQOL-36. The discriminant validity was satisfactory with a group of moderate and severe burden of pruritus for both dialysis samples. For scale reliability, the UP-Dial revealed excellent internal consistency (Cronbach’s α = 0.89 and McDonald’s ω = 0.90) and reproducibility (intraclass correlation 0.84–0.85) for both dialysis samples. Regarding psychometric properties, no statistically significant differences between dialysis samples were observed (all P > 0.05). Conclusions The findings reaffirm good measurement properties of the UP-Dial 14-item scale in haemodialysis and peritoneal dialysis patients with chronic pruritus. These suggest a transferability of the UP-Dial as a PRO measure in clinical trial and practice settings.