Advances in our understanding of uremic retention solutes, and improvements in hemodialysis membranes and other techniques designed to remove uremic retention solutes, offer opportunities to readdress the definition and classification of uremic toxins. A consensus conference was held to develop recommendations for an updated definition and classification scheme on the basis of a holistic approach that incorporates physicochemical characteristics and dialytic removal patterns of uremic retention solutes and their linkage to clinical symptoms and outcomes. The major focus is on the removal of uremic retention solutes by hemodialysis. The identification of representative biomarkers for different classes of uremic retention solutes and their correlation to clinical symptoms and outcomes may facilitate personalized and targeted dialysis prescriptions to improve quality of life, morbidity, and mortality. Recommendations for areas of future research were also formulated, aimed at improving understanding of uremic solutes and improving outcomes in patients with CKD.

Background

Uremia is a broad term that has been variably used to describe the buildup of metabolic waste products, such as urea, that occurs with diminished kidney function. Along with the retention of metabolic waste products, patients with advanced kidney disease typically experience a constellation of symptoms that may include nausea, vomiting, fatigue, anorexia, muscle cramps, pruritus, mental status changes, and others, which lead to a reduced quality of life and excess morbidity and mortality. Given the retention of metabolic waste products with advanced kidney disease, there has been much interest in using dialysis techniques to remove these substances with the hope that symptoms and outcomes would also improve. However, this goal has only been partially achieved, and outcomes for patients with kidney disease remain suboptimal. Although our knowledge of solutes that build up with uremia has increased, there is a growing recognition that dialysis prescriptions (both hemodialysis and peritoneal) may not be effective in their removal. Furthermore, technological advances, such as the development of new hemodialysis membranes and the ability to perform high efficiency hemodiafiltration, enable the removal of molecules from the body up to a mass of approximately 50 kDa (1). Besides, other new technologies are being developed to remove toxins that build up with abnormal kidney function (2).