New comorbidity index helps predict post-transplant survival

Nov 6 2007

Patients awaiting liver transplantation who also suffer from other medical problems may face poorer survival after transplantation.

These comorbid problems, which include coronary disease, diabetes, chronic obstructive pulmonary disease (COPD), connective tissue disease and renal insufficiency, have been incorporated into a new modified comorbidity index which helps predict post-transplant survival. These findings are published in the November issue of Liver Transplantation, a journal by John Wiley & Sons. The article is also available online via Wiley Interscience.

Determining who receives the limited supply of donor organs is one of the greatest challenges facing the transplant community. Severity of illness is the main criteria for hopeful liver recipients, however it is not the only factor that influences post-transplant survival. In other medical fields, co-morbidities have been considered as relevant predictors of survival, but never among the liver transplant community.

To address this paucity in the literature, researchers, led by Michael Volk of the University of Michigan sought to determine if the Charlson Comorbidity Index (CCI) would predict long-term survival after liver transplantation.

They conducted a retrospective study of 624 patients who underwent liver transplantation at the University of Michigan Hospital between 1994 and 2005 (to obtain a median follow-up of 5 years). They collected demographic, clinical and laboratory data for each patient, but focused on the nine comorbidities comprising the Charlson Comorbidity Index. These include congestive heart failure, coronary artery disease, diabetes mellitus, peripheral vascular disease, cerebral vascular accident, COPD, connective tissue disease, renal insufficiency and malignancy.

Forty percent of the patients had one or more comorbidities prior to transplantation. After statistical analysis, the researchers found that coronary disease, diabetes, COPD, connective tissue disease, and renal insufficiency were all independent predictors of poorer post-transplant survival. The researchers then recalibrated the CCI using this information, to create the CCI-OLT. This new index predicted post-transplant survival as well or better than other available models which use recipient characteristics like age, race, BMI, and etiology of liver disease.

“Our study shows that comorbidities play an important role in determining post-transplant survival,” the authors report. “This information will be useful when counseling patients with comorbidities about outcomes after transplantation.”

The study was limited by the fact that it was a single center, retrospective cohort study, and the researchers were not able to determine to what extent the comorbidities were manifestations of advanced liver disease. Still, the researchers demonstrated the usefulness of the modified comorbidity index for predicting post-liver-transplant. “In the future,” they conclude, “the addition of comorbidities to multivariable models may be useful in developing new allocation algorithms which incorporate the likelihood of post-transplant survival.”

An accompanying editorial, by Richard Freeman of the New England Medical Center, lauds the authors for their novel approach, though he cautioned that it remains to be seen if these results can be replicated. He writes that it is also somewhat disappointing that the CCI-OLT index was no better at predicting outcome than most of the other models already published.

Still, he reports, the mathematical model present by Volk and colleagues, “can help estimate ahead of time what might be correct choices for patients when the call comes in the middle of the night.”