Association of advanced age with concentrations of uraemic toxins in CKD.

To our knowledge, there are no studies on advanced chronic kidney disease (CKD) analysing the impact of ageing on serum concentrations of uraemic toxins while adjusting for renal function. Knowledge of this feature, however, could influence prognostic assessment and therapeutic decision-making, e.g. about when to start dialysis or how intensive it should be. Indeed, the slowing down of metabolism with age may result in lower uraemic toxin concentrations, hence reducing their toxic effects. In this case, a later start of dialysis or less intensive dialysis may become justified in an already fragile population that might enjoy a better quality of life without a survival disadvantage with conservative treatment. We assessed the impact of advancing age on uraemic solute concentrations [blood, urea, nitrogen (BUN), uric acid, creatinine, asymmetric and symmetric dimethylarginine (ADMA and SDMA), β2-microglobulin and a large array of protein-bound solutes] by matching 126 maintenance haemodialysis patients subdivided into two age-groups, younger vs. older (using the median as cut-off: 72 years). Concentrations were compared after age stratification and were matched with patient and dialysis characteristics. In addition, 93 non-dialysed CKD patients (median as cut-off: 70 years), with a comparable average estimated glomerular filtration rate (eGFR) between younger and older age-groups, were analysed. In haemodialysis patients, carboxy-methyl-furanpropionic acid (CMPF) levels were markedly higher and BUN and uric acid borderline lower in the older age-group. All other solutes showed no difference. At multifactor analysis, the concentration of several uraemic toxins was associated with residual renal function and protein intake in the overall haemodialysis group and the younger group, but the association with most solutes, especially those protein-bound, was lost in the older age-group. No differences were found in non-dialysed CKD patients. It was concluded that in this CKD population concentrations of uraemic toxins did not change substantially with calendar age.