That Strange Dialysis Conundrum - Selection bias .. 'Cherry picking' .. or Optimum HD for those who can
Dialysis – indeed, the whole modality realm of renal replacement – presents us with a strange conundrum.
We just know that dialysis is—for almost all except, perhaps, the very old, frail or infirm—a better option than conservative therapy for both longevity and wellbeing . But…has there ever been a randomized control trial (RCT) of dialysis vs. conservative therapy to “prove” this? No, there has not—nor will one ever likely be done.
We just know that transplantation—for the young, fit and less co-morbid—offers better wellbeing than does dialysis. But…has an RCT ever confirmed this? No, nor are we likely to conduct one, despite several recent papers that favorably compare the survival outcome of “matched” patient cohorts of home extended hour and frequency dialysis to those of deceased donor transplantation (1).
But then, when it comes to comparing the various modalities of dialysis, we lose the “certainty” plot. Suddenly, we seem not to know , or accept, which dialysis modality—or, more particularly, what modality setting: facility or home —yields the best outcomes. This is despite the wealth of multi-national, all-in, registry data and observational studies that support superior outcomes from home-based therapies—especially home hemodialysis. Aha, they say, the successful outcome studies in home dialysis are all because of “selection bias”!
Despite warmly embracing the superior outcomes of transplantation, as we should, we rarely acknowledge that the renal transplant cohort is one of the most highly medically selected groups on the planet. Every orifice is inspected, every organ is assessed, every biochemical, bacteriological and immunological cranny is probed. On the other hand, dialysis patients are, broadly, those who are deemed unfit or unacceptable for transplantation, though a minority will be transplant candidates awaiting a donor kidney. But, we do advise transplantation wherever possible and feasible…because it is “offering the best to the best”—and that’s the right thing to do.
Conversely, when dialysis patients are seen to do better at home—long regarded as the best option in dialysis—we hear long and loud complaints about “selection bias” . This, inexplicably, turns the “offering the best to the best” argument back against home dialysis patients, almost as if going home is in some odd way “cheating”.
Opposite to its use in transplantation, somehow, selection bias seems used as a criticism of and not as praise for home dialysis: they only ‘do better’ because they are ‘selected to do better’ . Meanwhile, those professionals who offer and encourage home dialysis are accused of “cherry picking” the best patients out of facility care. Well, if I am a cherry picker, so be it...and may I keep finding more cherries to pick.
In an effort to resolve this issue, a brave but ultimately unsuccessful RCT, the 2nd trial arm (FHN2) of the Frequent Hemodialysis Network Study group, attempted to provide an answer (2). Unfortunately, all this ill-fated trial managed to do was to further muddy the waters. I was asked to summarize this view for the September 6th, 2014 issue of the ASN publication, Kidney News(3).In the final analysis, FHN2 was hopelessly underpowered (only 1/3 rd of the required number could be recruited), the recruiting rules had to be changed mid-trial, and the home trial arm did not comply with trial requirements …yet, even with 1/3rd of ‘N’, near significance was achieved in favor of home extended hour dialysis. But, as reporting rules dictate, near significance is not significant, and the trial reported no advantage to the home arm over conventional facility hemodialysis. Piffle!
And, in truth, who cares if either transplant or dialysis patients are “selected”? If they can do better, they should be allowed to do better! We should be encouraging patients, facilitating them—in any way we can—to achieve their maximum lifestyle, wellbeing and survival potentials.
We should be moving heaven and earth to create the systems, practices and supports that will allow as many as possible to break out of the cycle of dependence, suppression, and regimentation that facility-based dialysis enforces on so many patients who, if encouraged, facilitated, and supported, would manage and do better at home.
The next time I hear an accusation of “cherry picking” dialysis patients for home hemodialysis, I will picture the beauty of a cherry tree in blossom, I will marvel at the number of cherries it can produce, and I will ponder how to best manage to pick them, every one.
Pauly RP, Gill JS, Rose CL et al. Survival among nocturnal home haemodialysis patients compared to kidney transplant recipients. Nephrol. Dial. Transpl. 2009; 24: 2915–19.
Rocco MV, Lockridge RS, Beck GJ et al. The effect of frequent nocturnal home hemodialysis: the Frequent Hemodialysis Network Nocturnal Trial. Kidney International (2011) 80, 1080–1091.
Agar J W M. Home Hemodialysis: Do We Need More Randomized Controlled Data? Kidney News. 6(9). September 2014.