The findings, according to researchers, suggest there may be a bias in the way donor kidneys are allocated.

Analyzing a decade's worth of national transplant data, researchers at Johns Hopkins University in Baltimore found that morbidly obese patients - those who are 100 or more pounds overweight-on the kidney transplant waiting list were 44 percent less likely to receive a donor organ as normal-weight patients.

There was no similar disparity seen among overweight or mildly obese patients, the researchers report in the Journal of the American Society of Nephrology.

"The results identify a potential bias in organ allocation that is not consistent with the goals of our allocation system," Dr. Dorry L. Segev, the lead researcher on the study, said in a statement.

In the U.S., the United Network for Organ Sharing (UNOS) oversees the allocation of donor organs. Segev and his colleagues based their findings on UNOS data for 132,353 patients on the waiting list for a kidney transplant between 1995 and 2006.

They found that even when they considered medical factors that affect a person's eligibility for a donor kidney-such as age or diabetes-the odds of receiving a transplant decline with the severity of a patient's obesity.

Waiting-list patients who were morbidly obese were the least likely to get a transplant. Similarly, those considered severely obese were 28 percent less likely to receive a donor kidney than normal-weight patients were.

In addition, when a donor organ did become available, the most obese patients were more likely than other patients to be "bypassed"-meaning their doctors were more likely to decline the offer of a kidney.

"It is possible that providers are bypassing obese patients and instead transplanting non-obese patients because they feel that kidneys are a scarce resource and they want the kidneys to go to the patients who will benefit most from them," Segev said.