Donor Sex and Size Important to Kidney Transplant Success Interview with:
Amanda Miller, MD, FRCPC

Dalhousie University
Transplant Nephrology What is the background for this study? What are the main findings?

Response: Earlier studies have shown that there may be a higher risk of kidney transplant failure if a kidney donor is smaller than their recipient. This may be due to increased strain on the relatively smaller transplanted kidney. Very few studies have investigated outcomes associated with donor and recipient weight mismatch measured directly by differences in body weight however. There is also a suggestion that sex mismatch between kidney donor and recipient may lead to worse outcomes post-transplant, however results from earlier studies have been controversial and conflicting. The combined effect of weight and sex matching/mismatching between kidney donor and recipient (two very important and physiologically relevant factors) has not been rigorously studied previously.

Thus, the aim of this study was to determine if receiving a kidney transplant from a smaller donor of the opposite sex would impact transplant outcomes. Accounting for other transplant variables, we demonstrated that if a kidney transplant recipient is more than 30 kg (66 pounds) heavier than the donor there is a 28% increased risk of the transplant failing compared to equally weighted donors and recipients. If the kidney is from a smaller donor of the opposite sex, the risk of transplant failure is further increased to 35% for a male receiving a kidney from a female donor, and 50% for a female receiving a kidney from a male donor. This risk is high and is similar to that when a recipient receives a kidney transplant from a donor who has diabetes; a known risk factor for kidney failure in the non-transplant population. What should readers take away from your report?

Response: This study highlights the fact that the specific pairing of a kidney donor and recipient’s weight and sex may be associated with a marked increase in kidney transplant failure. In our study, females receiving kidneys from smaller male donors (recipient weight 30 kg more than the donor) were at the highest risk of kidney graft loss, at rates approximating that seen for donors with diabetes. Currently, most algorithms for choosing a recipient of a deceased donor kidney do not consider these factors. While more research is required before including these variables in a recipient matching strategy, this study highlights the potential benefit of donor and recipient matching above and beyond current age and immunology-based protocols. What recommendations do you have for future research as a result of this study?

Response: This study highlights a potential kidney transplant survival advantage associated with optimal weight and sex pairing of kidney donors and recipients, however it is exploratory in nature and further study is certainly indicated. While donor-recipient weight and sex matching has the potential to improve the utility for a given kidney, at a population level there is a risk of inequity for certain individuals on the kidney transplant waitlist. For example, a weight and sex matching organ allocation strategy may disadvantage large female recipients, who may in turn face longer transplant waitlist times; a factor known to be associated with adverse outcomes. Prolonged waitlist times may potentially offset any benefit derived from strategic donor-recipient matching, and modelling studies are required to determine the risk/benefit ratio of instituting such an organ allocation program. Additionally, other non-immunologic factors may need to be considered in future analyses. Lastly, this was a retrospective analysis, and if donor-recipient weight and sex matching are to be considered, these findings should be validated prospectively. Is there anything else you would like to add?

Response: The main limitation of this study is the fact that this was a retrospective observational analysis. Data was obtained from the Scientific Registry of Transplant Recipients (SRTR) which is a large-scale, nationally representative database which has been used in numerous earlier studies and is felt to be a robust record of transplant outcomes in the United States. Like any retrospective study however, there is potential for miscoding or misclassification of data. However any errors in weight or sex coding would be expected to be distributed evenly and thus would be unlikely to bias results. Additionally, observational studies can demonstrate associations between different variables, but they do not prove causation, and this fact must be remembered when interpreting any study results.

The study authors have no disclosures. Thank you for your contribution to the community.


Amanda J. Miller, Bryce A. Kiberd, Ian P. Alwayn, Ayo Odutayo, and Karthik K. Tennankore
Donor-Recipient Weight and Sex Mismatch and the Risk of Graft Loss in Renal TransplantationCJASN CJN.07660716; published ahead of print March 30, 2017, doi:10.2215/CJN.07660716

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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Last Updated on April 4, 2017 by Marie Benz MD FAAD