Activated carbon may allow additional small solute clearance, particularly protein-bound solutes, a new study finds. If clinical benefit is proven, sorbents such as activated carbon might be integrated into dialysis circuits.

In their first experiment, Seolhyun Lee, MD, of Veterans Affairs Palo Alto Healthcare System in California, and colleagues collected batches of spent dialysate from several patients and passed each batch through a block containing 200 g of activated carbon. Metabolomic analysis showed that activated carbon adsorbed 216 of 264 identified uremic solutes from the dialysate, essentially renewing it for further use. Activated carbon was particularly effective in adsorbing uremic solutes that bind to plasma proteins, the investigators reported. Adsorptive capacity decreased, however, after processing of large dialysate volumes. Further, some uremic solutes, such as methylguanidine, were released by the carbon block.

In a second experiment, Dr Lee’s team performed in vitro dialysis incorporating the carbon block. Activated carbon increased the clearance of the protein-bound solutes indoxyl sulfate and p-cresol sulfate by 77% and 73%, respectively, at a low dialysate flow rate of 200 mL/min, but increased the clearance of the unbound solute phenylacetylglutamine by only 30%. There was no increase in urea clearance.

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“Activated carbon adsorbs many but not all uremic solutes,” Dr Lee and colleagues wrote in the Journal of the American Society of Nephrology. “Introduction of activated carbon into the dialysate stream increased the clearance of those solutes that it does adsorb.”

In an accompanying editorial, Mengyao Tang, MD, of Brigham and Women’s Hospital and Sahir Kalim, MD, MMSc, of Massachusetts General Hospital, both in Boston, praised the team for adding important incremental knowledge toward the “daunting” task of kidney replacement through dialysis.

“From [medium cutoff] dialyzers to dialysate processing with sorbents, each of these finite improvements to solute clearance on hemodialysis, if proven safe and effective, will hopefully see benefits magnified when used synergistically,” they wrote.

Which solutes should be targeted and for what clinical benefit remains unclear and warrants further research, according to the editorialists.

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Lee S, Sirich TL, Blanco IJ, Plummer NS, Meyer TW. Removal of uremic solutes from dialysate by activated carbon. Clin J Am Soc Nephrol. Published online July 14, 2022. doi:10.2215/CJN.01610222

Tang M, Kalim S. Novel approaches for the removal of uremic solutes. Clin J Am Soc Nephrol. Published online July 14, 2022. doi:10.2215/CJN.06860622