Associations between small and middle molecules clearance and the change of cognitive function in peritoneal dialysis

Background Uremic toxins have been suspected as potential contributors for cognitive impairment in peritoneal dialysis (PD) patients. However, associations between the clearance of serum small and middle molecules and the change of cognitive function were not fully explored and then we explored this issue in the present study. Method A total of clinically-stable 222 patients on PD were enrolled and then followed up for 2 years in this single-center prospective cohort study. Small and middle molecules clearances were examined by urea clearance (Kt/V), creatinine clearance (Ccr) and beta-2 microglobulin (B2M) clearance via dialysate and urine at baseline and after 2 years. Global and specific cognitive impairment were measured at baseline and after 2 years. Modified Mini-Mental State Examination (3MS) was assessed for global cognitive function, trail-making tests A and B for executive function and subtests of the battery for the assessment of neuropsychological status for immediate and delayed memory, visuospatial skills and language ability. Results The median of total Kt/V, Ccr and B2M clearance were 1.89, 53.2 l/w/1.73 m(2) and 17.5 l/w/1.73 m(2), respectively at baseline. The prevalence of global cognitive impairment was 12.3% for 222 patients and 15.4% for the remained 130 patients after 2 years. At baseline, total Kt/V was independently positively associated with delayed memory function. Total and dialysate beta-2 microglobulin clearance was positively associated with 3MS scores and negatively with completion time on trail A after multivariate adjustment. At 2 years, we observed a significant difference in the changing trend of 3MS scores between groups divided by total B2M clearance (P = 0.033), which still maintained to be meaningful after multivariate adjustment (P = 0.024). Patients with total B2M clearance > 19.0 l/w/1.73 m(2) got significant improvement on their 3MS scores (P = 0.005). Patients divided by total Kt/V or Ccr were not significantly different in the trends of general and any specific cognitive function during the follow up. Conclusion The higher middle molecules clearance independently correlated to better performance on general cognitive and executive function in PD patients, which also predict an improvement in general cognitive function during the follow up.