Poor allograft quality may not be the only reason for turning down a donor kidney, according to a new study published online in the American Journal of Transplantation — factors as unrelated as the stature of the donor or weekend procurement can affect acceptance.

Allograft quality is essential for a positive transplant outcome, of course, and selectivity can reduce failure and ensure graft survival. This new study suggests clinicians may be turning down kidneys for reasons other than quality. Rejecting suitable kidneys may increase an already-long transplant waiting list.

More than 116,000 people need a life-saving organ transplant, according to the U.S. Department of Health and Human Services' Organ Procurement and Transplantation Network; more than 75,000 are on the active waiting list.

Despite significant gains in medicine, technology and awareness of organ donation and transplantation, there is still a substantial gap between supply and demand. To close this gap, researchers are working toward understanding the patterns of organ acceptance and reducing organ discard.

The Kidney Donor Risk Index (KDRI) indicates the relative risk of graft failure following kidney transplant as a single number, expressed as a cumulative percentage scale. Kidneys from a donor with a KDPI of 70 percent, for example, will have a higher relative risk of graft failure than 70 percent of recovered kidneys.

KDPI arrives at this number through analysis of a variety of donor factors, such as age, height and weight, history of hypertension, history of diabetes, cause of death, serum creatinine and HCV status. A higher KDPI is associated with poorer donor quality and decreased expected longevity.

There is currently a paucity of information about how donor factors, geographic location and timing of procurement affect organ offer decisions. Jordana B. Cohen, M.D., from the University of Pennsylvania in Philadelphia hoped to shed light on how characteristics unrelated to allograft quality may lead to organ rejection.

The researchers included 47,563 deceased donor kidney match-runs from 2007-2013 into a retrospective cohort study. The investigators followed the recipients of those kidney transplants through June 1, 2015, date of allograft failure or date of death — whichever came first.

They addressed each kidney as a separate match-run, so if the donor was listed as having kidneys accepted at position one and position two, the scientists would consider both kidneys as position one for the purposes of this study. Match-run data were not available for discarded organs.

Since the researchers could not include discarded organs in their organ acceptance position analysis, they performed separate studies in which they compared donor characteristics and other factors between discarded organs and all transplanted organs. In the secondary analysis, the scientists evaluated the outcomes of delayed graft function, all-cause allograft failure and mortality.

The scientists found an association between certain characteristics unrelated to allograft quality and later acceptance in the match-run. These characteristics include procurement over a holiday or weekend and shorter donor stature.

The researchers also found an association between Public Health Service (PHS) increased-risk donors organs and later acceptance in the match-run, at an adjusted odds ratio of 2.49. The authors of the study note that, based on risk factors such as recent incarceration, intravenous drug use or prostitution, PHS increased-risk donors are determined to be at increased risk for human immunodeficiency virus (HIV), hepatitis B virus or hepatitis C virus infection.

While the results of the study support a correlation for later acceptance in the match-run with delayed graft function, it did not show a correlation with all-cause graft failure.

"Interventions are needed to reduce turndowns of viable organs, especially when decisions are driven by infectious risk, weekend or holiday procurement, geography or other donor characteristics unrelated to allograft quality," the authors wrote.