(ABC NEWS) -- If Sarah Murnaghan were 12 years old, she would be at the top of the adult lung transplant list because she only has weeks to live and a lung transplant would as-good-as cure her of cystic fibrosis.
But she's not 12, and if she doesn't get new lungs, she might not even make it to 11.
"We are not asking for preference for Sarah, we are asking for equality," Sarah's mother, Janet Murnaghan, said in a press release. "We strongly believe Sarah should be triaged based on the severity of her illness, not her age."
The Murnaghan family of Newrown, Pa., is fighting a little known organ transplant policy that is effectively pushing 10-year-old Sarah to the bottom of the adult transplant waiting list because it mandates that adult lungs be offered to all adult patients before they can be offered to someone under 12 years old.
Sarah has been on the pediatric waiting list for new lungs for 18 months, but since there are so few pediatric organ donors, there hasn't been a match. She's been living at Philadelphia Children's Hospital for two months connected to a machine to help her breath, Sarah's aunt, Sharon Ruddock, told ABCNews.com.
There were only 11 lung donors between 6 and 10 years old and only two lung transplants in that age group in 2012, according to an Organ Procurement and Transplantation Network statement.
However, since Sarah was eligible for an adult lung transplant, her family was both horrified and excited when her condition rapidly deteriorated earlier this month because they thought it meant she would get bumped to the top of the adult waiting list, Ruddock said.
"A week went by with nothing, no offers," Ruddock said. "They said, 'Well, you're not at the front of the line. It goes to all adults, and if all the adults turn them down, the lungs go to the kids.'"
Patients with cystic fibrosis, a genetic condition that damages the lungs, have an average life expectancy of 31 years old, said Dr. Devang Doshi, a pediatric lung specialist at Beaumont Children's Hospital in Michigan who has not met Sarah. But if they get a lung transplant, the condition is essentially cured.
"It's a very disheartening thing to hear and read about because you've got a child in desperate need of a transplant to survive ... and people less qualified in terms of severity are able to get that organ instead of this child because of what's in place," Doshi said. "From a medical standpoint, we look at these types of hurdles and obstacles and sometimes get frustrated with the system."
So Sarah's family started an online petition at change.org to persuade the Organ Procurement and Transplantation Network to change its policy. So far, they've gathered about 40,000 signatures.
The organization, which falls under the U.S. Department of Health and Human Services, responded on Monday that it can't make an exception for Sarah.
"OPTN cannot create a policy exemption on behalf of an individual patient, since giving an advantage to one patient may unduly disadvantage others," the statement read.
Doshi said he thinks children under 12 years old should be considered with the adult patients and awarded organs based on how severe their conditions are. Adult lungs may not perfectly fit child patients, but they can be used to save multiple children. One of his 6-year-old patients' got a partial lung donation from her mother several years ago in a last ditch effort to save her life.