Journal Club: dialysis time, not the critical factor in graft survival

One of the inherent truths in transplant is that the longer someone is on dialysis the worse the outcome after transplant. Patient with higher dialysis vintage prior to transplant are more likely to lose their graft and die following transplant. This was first shown by Cosio Et al. and subsequently verified by other researchers.

Cosio's primary figure showing dramatically increased mortality with increasing time on dialysis

Though Cosio et al. was the first (?) to find this association the most elegant data comes from Meier-kreiesche, Et al. who looked at graft survival when a paired sets of cadaveric kidneys is donated to recipients with differing duration of dialysis. By looking at paired kidneys they were able to neutralize any confounding factors from the donor. The primary analysis looked at kidneys that were split between one recipient with less than 6-months of dialysis and another with more than 2-years of dialysis. The end-point was graft survival:

They also calculated patient survival and they likewise found a significant splay based on time on dialysis:

Five- and ten-year unadjusted overall patient survival for paired kidneys was 89% and 76%, respectively, in the group on dialysis less than 6 months compared to 76% and 43%, respectively, in the group on dialysis for more than 2 years (P<0.001 each).

The obvious implication was that dialysis was bad for you. The longer you were on dialysis the more baggage you were carrying at the time of transplant and that baggage comes back to haunt the recipient with a shorter life and shorter kidney survival. From the conclusion:

...the longer patients wait on dialysis for a transplant the longer patients are exposed to the chronic effects of end-stage renal failure and dialysis. It is well documented that patients on dialysis have alterations in the concentration of a number of substances (e.g., homocysteine, advanced glycosylation end products, and lipoproteins) that may predispose these patients to both cardiovascular and renal allograft vascular damages. In addition, the poor nutrition, chronic in- flammatory state, altered immunologic function, and inade- quate clearance that often accompanies patients with ESRD on dialysis may predispose these patients to poorer toler- ance to the immunosuppressive agents after transplantation.

On our journal club last week we looked at a study by Schold, et al. that analyzed time on dialysis prior to transplant by dividing it into time prior to wait list and time after being listed. They found that all of the risk from prolonged dialysis comes from the time prior to being placed on the transplant wait list:

The data was more dramatic for graft loss than for mortality. The intersting part of this is trying to explain this discrepancy.  Why would time on dialysis prior to wait listing be any different that time on dialysis after wait listing? There is no biological difference so the authors conclude that the difference must be in a subtle, previously unmeasured difference in co-morbidity or access to care. The authors go on to pre-suppose that efforts to reduce patient exposure to dialysis may not yield the benefits one might expect if these other factors are not also corrected.