Cystic fibrosis (CF) patients with low body weight are not at increased risk of mortality after a lung transplant, compared to people with other lung diseases who require the transplant, a new study reports.

The findings were described in the study “Underweight patients with cystic fibrosis have acceptable survival after lung transplantation: a UNOS registry study,” which was published in the journal Chest.

Lung transplant (LTx) is often required to improve the quality of life and survival of people with end-stage pulmonary diseases. Candidate selection for the procedure typically takes into account the patient’s lung disease prognosis, and their expected survival outcome compared to the overall population who need LTx.

One of the LTx criteria taken into account is a person’s pre-operative body mass index (BMI). Previous studies have found a link between low pre-operative BMI and longer hospital stays, increased risk of death due to post-transplant infection, and increased overall risk of mortality.

People with CF in particular are often underweight, and advanced lung disease and low BMI have been associated with worse post-transplant outcomes in CF patients. At present, a BMI lower than 17 or 18 kg/m2 in CF patients is considered a contraindication for undergoing LTx at many centers.

“However, how the post-transplant survival of CF patients with BMI below usual exclusion thresholds compares to the general LTx candidate population is unknown,” the researchers wrote.

Thus, a team led by these researchers, at the University of Washington, assessed the post-LTx survival of CF patients with BMI lower than 17 kg/m2 compared with CF patients with normal weight, and other patients with chronic lung diseases requiring a LTx.

The researchers used the United Network for Organ Sharing (UNOS) registry to gather data from 13,510 patients, including 2,195 with CF, 4,858 with chronic obstructive pulmonary disease (COPD), and 6,457 with idiopathic pulmonary fibrosis (IPF), who received LTx between June 2005 and November 2015.

Patients included in the study were older than 12, and had their first LTx. In the group of CF patients, 16% (352 patients) had a BMI lower than 17 kg/m2 at the time of LTx.

Results showed that the median post-LTx survival time was 7.0 years for CF patients with BMI lower than 17 kg/m2, compared to 8.2 years for CF patients with BMI higher than or equal to 17 kg/m2. However, after running a statistical analysis, the researchers did not see an increased mortality risk for CF patients with BMI lower than 17 kg/m2.

The team also found that CF patients with BMI lower than 17 kg/m2 had an 88% estimated likelihood of surviving their first year post-LTx, which was close to the 89% estimated likelihood found in CF patients with BMI higher than or equal to 17 kg/m2.

For CF patients who survived their first year after surgery, the median post-LTx survival time was 7.8 years if their BMI had been lower than 17 kg/m2 at the time of surgery, and 9.5 years if their BMI was higher than or equal to 17 kg/m2. In contrast, the median survival time post-LTx for patients with COPD was 6.9 years, and 6.8 years for IPF patients.

Five years post-TLx, CF patients with BMI lower than 17 kg/m2 had an estimated survival rate of 54%, which — although it was lower than the 61% found in patients with BMI of at least 17 kg/m2 — was still similar to that of patients with COPD (56%) and IPF (53%).

Overall, “the current study highlights reasonable post-transplant survival for a cohort of underweight individuals with CF who, based on previous considerations, may be unjustifiably excluded from LTx at most centers in the U.S.,” the researchers wrote.

Based on the results, the team proposed that a BMI lower than 17 kg/m2 “as a single risk factor in the CF population should not be treated as an absolute contraindication to LTx.”