A review published online July 15 in Kidney International recommends that Kt/V is still a useful metric to measure dialysis adequacy.

John T Daugirdas, MD, from the University of Illinois College of Medicine, in Chicago, wrote that there is not enough data to show that increased removal of protein-bound uremic solutes impacts outcomes. But there is data that shows the usefulness of Kt/V, which measures the removal of water-soluble urea, such as the 1985 reanalysis of the National Cooperative Dialysis Study (NCDS) that showed a strong effect of dose calculated as Kt/V on short-term outcome.

Another recent review published in Kidney International argued that Kt/V is too simple a concept for the complexities of uremia and of today’s dialysis.

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Daugirdas also notes that there is also a lack of data that shows the positive effects of more frequent dialysis. “In the FHN [Frequent Hemodialysis Network] trials, there was no effect of frequent dialysis, including frequent and long dialysis, on nutrition or control of anemia, outcomes expected to be sensitive to uremic toxin removal; the main benefit appeared to be better volume control.”

Daugirdas also expresses skepticism about observational data that shows benefits of more frequent dialysis. “In contrast to randomized trials, analysis of dialysis dose (including time) in observational data sets is rendered difficult to impossible because of the very strong effect of dose-targeting bias that results in better survival in patients meeting a given dose target, whether it be Kt/V or session length, compared with patients who are not meeting the target,” Daugirdas wrote. “The magnitude of dose-targeting bias can be enormous, and is much larger than possible biological effects of differences in administered dose.”

However, Daugirdas does say there is data to support the idea that the dialysis dose should be scaled to body surface area, rather than to total body water. “Based on a single, prespecified analysis of the HEMO study, where women, but not men, were apparently benefitted from a higher dose of dialysis, and also on observational data, rescaling of dialysis dose to body surface area has been advocated.”

“In summary, there are aspects of hemodialysis adequacy in 2015 that clearly extend beyond Kt/V urea; however, the few pieces of hard outcomes evidence that we do have suggest that monitoring small molecular clearance, as measured by Kt/V and its derivative, standard Kt/V, perhaps rescaled to body surface area, remains a useful metric to monitor treatment, especially in the overwhelming majority of patients receiving dialysis on a 3/week schedule,” Daugirdas concludes.

The full review is published by Kindey International, and is available on its website.