Supplementary Material for: Increased Levels of Total <b><i>p</i></b>-Cresylsulfate Are Associated with Pruritus in Patients with Chronic Kidney Disease

<b><i>Background:</i></b> Pruritus is a common and distressing symptom that affects patients with chronic kidney disease (CKD). Indoxyl sulfate (IS) and<i> p</i>-cresylsulfate (PCS) are uremic toxins with similar protein binding, dialytic clearance, and proinflammatory features. Pruritus in CKD may correlate better with uremic toxins than the glomerular filtration rate (GFR), suggesting that uremic toxins either in the central nervous system or peripherally may play an important role in the pathophysiology. <b><i>Objective:</i></b> We sought to investigate the potential contribution of serum total IS and PCS to the pathogenesis of pruritus. <b><i>Methods:</i></b> The serum levels of total IS and PCS concentrations were measured in all patients by using the Ultra Performance LC System. The characteristics of pruritus were assessed using a visual analog scale score and an interview questionnaire. <b><i>Results:</i></b> Among the 320 CKD patients, 35% had pruritus. The patients with pruritus were older and had a higher frequency of diabetes mellitus, higher uric acid, calcium, phosphorus, creatinine, high-sensitivity C-reactive protein, and total IS and PCS levels, and lower albumin concentrations and estimated GFR (eGFR) than those without pruritus. Increasing concentrations of total PCS were independently and significantly associated with pruritus. Multiple logistic regression analysis revealed total PCS as an independent association factor for pruritus, even after full adjustment of known biomarkers. Furthermore, serum total PCS levels were positively associated with calcium, phosphorus, blood urea nitrogen, creatinine, and white blood cell count, and negatively associated with eGFR, hemoglobin, and hematocrit. <b><i>Conclusion:</i></b> Our results indicate that total PCS may play a role in the pathogenesis of pruritus