A BMI below 18.5 is underweight, and a BMI between 18.5 and 24.9 is considered a healthy weight.
A BMI between 25 and 29.9 is overweight, and a BMI of 30 or higher is obese. Severe obesity includes a BMI of 35 to 39.9 and extreme obesity is a BMI of 40 or higher.
During the course of this study, 14 percent of those on the wait list died, and 4 percent were removed from the wait list.
Meanwhile, 12 percent of those who received a transplant died during the study follow-up.
However, the survival rates varied within each BMI category after the researchers took into account the patients' age, gender, race, medical history, length of time on the wait list and cause of their end-stage renal disease (the reason they needed a kidney).
For example, among transplant recipients who received a kidney from a standard criteria donor (a person under age 50 who had brain death), extremely obese recipients were 48 percent less likely to die after getting the kidney.
In comparison, recipients in other BMI categories lower than extreme obesity had a 66 percent reduction in their risk of death.
Those who received a kidney from a living donor were 66 percent less likely to die, regardless of their weight.
For obese diabetes patients aged 50 or older, getting a kidney transplant did result in better chances of survival unless they were African American.
For blacks with a BMI of 40 or higher, getting a transplant did not improve their chances of survival.
Overall, extremely obese patients appeared to be more likely to survive if they got a kidney transplant, but their chances were not as high as those of patients who were not extremely obese.
"Our findings support the use of transplantation from all donor sources in most obese patients, but highlight the use of living donor transplantation as a strategy to increase the survival benefit of transplantation in most obese patients," the authors wrote.
According to dailyRx expert Michelle Segovia, of the Texas Organ Sharing Alliance, kidneys are among the most needed organs.
"Out of the 118,000 men, women and children awaiting an organ transplant, more than 96,000 wait for kidneys," Segovia said. "While kidneys can be donated from living and deceased donors, many of those waiting will never get the opportunity to receive a second chance at life because of the drastic organ donor shortage."
She said that ordinary individuals can be a part of the solution to that problem.
"We have the power to change that. Please ensure your decision to be a deceased donor is registered at www.DonateLife.net and discuss the decision with your family," Segovia said. "For those wishing to be a living kidney donor, please contact your area transplant center."
This study was published July 25 in the American Journal of Transplantation.
The research was funded by the Kidney Research Scientist Core Education and National Training Program. The authors declared no conflicts of interest.