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Longer storage of red blood cell (RBC) units was associated with longer transplant survival in kidney transplant patients receiving early transfusions, a retrospective study in France found.

Among 3,483 kidney recipients who received RBC transfusions within 14 days posttransplant, each additional day of RBC storage was associated with a non-significant 1% reduction in the risk for transplant failure (P=0.06).

But compared with transfusions with RBC units stored for less than 20 days, transfusions with an RBC unit stored for 20 or more days were associated with a 2.1% absolute increase in transplant survival at 1 year and 6% at 5 years (HR 0.81, 95% CI 0.79-0.84, and HR 0.75, 95% CI 0.73-0.77, P=0.03), reported Emilie Gaiffe, PhD, of Franche-Comté University in Besançon, France, and colleagues in .

"This association was robust and persisted in all sensitivity analyses," Gaiffe and colleagues wrote. "Moreover, the size of the association is large, since such a transfusion policy may spare one graft loss in the first 5 years posttransplant for 14 patients receiving transfusions during the first 2 weeks after transplant."

Transplant failure was defined in the study as graft loss or death with a functioning graft, and graft loss was defined as a return to dialysis or re-transplant.

Associations between RBC storage and patient outcomes after transfusion have been long debated, Gaiffe and co-authors noted. Previous studies have reported mixed findings on and patient . RBC characteristics may change depending on a variety of factors which are not fully understood, the researchers added.

One effect of longer RBC storage sometimes seen as detrimental may actually help in kidney transplantation, observed Jason Acker, PhD, MBA, of the University of Alberta and a senior scientist at Canadian Blood Services in Edmonton, who wasn't involved with the study.

"We know the longer we store blood after it's donated, those immune cells that come from the donor -- after about 14 to 21 days, they disappear from that blood product, they degrade," Acker told 乌鸦传媒. "Older blood, perhaps, has fewer immune cells because it's been stored so long, partly affecting the outcome."

While non-randomized, observational studies are becoming more precise as data quality improves, they are always subject to confounders, Acker noted.

"Studies like this shouldn't be causing radical changes in transfusion practices; [there's] additional data that we need before we move down that path," he said. But "there are blood products that are probably safer for certain kinds of patients, and that's what research like this is trying to show, that there's perhaps more precise ways of doing transfusions."

Gaiffe and colleagues used data from France's national transplant registry, CRISTAL. Patients with a first kidney transplant graft from 2002-2008 and a RBC transfusion within 14 days of transplant were included. Follow-up was from inclusion on the waiting list to graft loss, death, or data retrieval in June 2016.

Graft failures within 15 days were excluded. Researchers collected data on blood donor demographics and blood product characteristics for each RBC transfusion. Patients could have more than one RBC transfusion from more than one donor, but characteristics specific to each donor and transfusion were accounted for.

The median age of patients was 53, and 55.4% were male. Median BMI was 23.6, and 86.3% of patients were on dialysis before transplant. Most patients (95%) received an organ from a deceased donor. Median follow up was 7.8 years, median number of RBC units transfused was two, for a median of one episode, which was defined as consecutive transfusions with intervals no more than 48 hours. The mean time for RBC transfusion was 4.6 days, and most patients received at least one unit from an opposite-sex donor.

Blood donor age was associated with risk of transplant failure, as were the number of transfusion episodes, RBC units per patient, and the delay between transplant and first RBC unit transfusion.

Limitations included the use of multiple transfusions, which may have increased the likelihood of receiving a fresher RBC unit, though the researchers adjusted for number of units and transfusion episodes. The association of time between transplant and transfusion with increased transplant failure also may have been influenced by differences in the context and indication of the transfusion.

Data on donors including race and ethnicity, previous pregnancies, and genetics were not collected and may have influenced RBC characteristics in storage, Gaiffe and colleagues acknowledged. Other unmeasured variables also may have affected graft failure.

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