"In clinical transplantation, we generally don't assume that organs from male and female donors have inherent differences affecting long-term outcomes, but our data suggest that there are important differences which must be taken into account," said Eric Weiss, M.D., first author of the study and a post doctoral research fellow in the Division of Cardiac Surgery at The Johns Hopkins University Medical Institutions in Baltimore, Md.
For the study, the researchers analyzed data from the United Network of Organ Sharing (UNOS), identifying 18,240 patients who received their first orthotopic (replacing a failing organ with a healthy one) heart transplant between 1998 and 2007. In this dataset, patients were followed for 10 years, with the average follow-up time being 3.4 years.
Patients were sorted into four groups: male donor with male recipient, female donor with male recipient, male donor with female recipient, and female donor with female recipient.
Overall, 71 percent were matched by gender to their donor (77 percent of male recipients and 51 percent of female recipients). Twenty-five percent of patients died during the study.
The researchers found that matching donor and recipient by gender resulted in 13 percent lower risk of graft rejection within the first year; 14 percent lower rate of graft rejection over the study period; 25 percent drop in 30-day death rate; and 20 percent lower one-year death rate.
Statistical modelling revealed that the greatest chance for death during the study occurred when pairing a male donor with a female recipient, which made the risk of death an estimated 20 percent higher compared to a male donor with male recipient.
The most successful transplants occurred between male recipients and male donors, when the cumulative chance for survival was 61 percent.
"These results fit with our hypothesis that sex matching in heart transplantation leads to improved survival rates. We hypothesized that we would see a big difference in the short-term survival - which we did, most likely because of heart-size issues - but what was interesting was the substantial difference in the long term, as well," said Weiss.
The study has been presented at the American Heart Association's Scientific Sessions 2008.