Survival tree and meld to predict long term survival in liver transplantation waiting list

1 Survival tree and meld to predict long term survival in liver transplantation waiting list Emília Matos do Nascimento a, Basilio de Bragança Pereira a,b, *, Samanta Teixeira Basto b, Joaquim Ribeiro Filho b aFederal University of Rio de Janeiro, COPPE - Postgraduate School of Engineering, Rio de Janeiro, Brazil bFederal University of Rio de Janeiro, School of Medicine and HUCFF - University Hospital Clementino Fraga Filho, Rio de Janeiro, Brazil _________________________________________________________________________________________ Abstract Background: Many authors have described MELD as a predictor of short-term mortality in the liver transplantation waiting list. However MELD score accuracy to predict long term mortality has not been statistically evaluated. Objective: The aim of this study is to analyze the MELD score as well as other variables as a predictor of long-term mortality using a new model: the Survival Tree analysis. Study Design and Setting: The variables obtained at the time of liver transplantation list enrollment and considered in this study are: sex, age, blood type, body mass index, etiology of liver disease, hepatocellular carcinoma, waiting time for transplant and MELD. Mortality on the waiting list is the outcome. Exclusion, transplantation or still in the transplantation list at the end of the study are censored data. Results: The graphical representation of the survival trees showed that the most statistically significant cut off is related to MELD score at point 16. Conclusion: The results are compatible with the cut off point of MELD indicated in the clinical literature. Keywords: Survival tree; Conditional inference trees; Recursive partitioning; MELD; Liver transplantation waiting list; Long term mortality prediction

• Corresponding author. Tel.: +55-21-25622594 E-mail address: basilio@hucff.ufrj.br (B.B. Pereira)

2 What is New

• MELD score cut off to predict long term mortality in liver transplantation waiting list was statistically evaluated for the first time.
• Survival Analysis Tree and MELD was used to predict long term mortality.

1. Introduction The Model for End-Stage Liver Disease (MELD) score was described as a short term mortality index used to predict three month mortality in patients who underwent transjugular intrahepatic portosystemic shunt (TIPS) insertion [1]. It was subsequently applied to allocate liver grafts in liver transplantation list in the United States and several countries, since February 2002 [2]. Many countries use subjective local criteria or UNOS based policy to allocate liver grafts according to liver disease severity [3]. In Brazil, liver transplantation waiting list was organized according to a chronological system until June, 2006 [4]. The liver transplantation waiting list time varies significantly among various centers but usually reflect a gap between the donor liver pool and the demand for transplant [5]. The longer waiting time results in a higher mortality rate [6]. It is important to identify those patients with the worst outcome. There are several factors related to liver transplantation waiting list mortality as age, gender, blood type and disease etiology [7]. Many authors have described MELD as an independent tool related to short term mortality in the transplantation waiting list and tried to determine a threshold to assess prognosis and mortality in this setting [8,9]. However MELD score accuracy to predict long term mortality has not been statistically evaluated in the past. The aim of this study was to analyze the MELD score as a predictor of long term mortality using a Survival Analysis Tree and to establish a MELD cut off point that better predicts this long term mortality. Cut off points of other covariates are also evaluated and their interactions with MELD is also analyzed. The data base and methods are presented in section 2. Section 3 presents the recursive partitioning method. The results and conclusion are presented in sections 4 and 5 respectively.

3 2. Data base and methods From November 1997 to July 2006, all patients in the liver transplantation waiting list were evaluated for inclusion in the study. Patients with incomplete data for MELD calculation were excluded and 529 were included. Data were obtained from the patient inclusion registration form and from the hospital’s internal system of patient registration (Medtrack) and organized in excel for posterior analysis.
The variables obtained at the time of liver transplantation list enrollment and considered in this study are: sex, age, blood type, body mass index, etiology of liver disease, hepatocellular carcinoma, waiting time for transplant (in days) and MELD. The formula for the MELD score [1] is
3.8loge(bilirubin[mg/dL]) + 11.2loge(INR) + 9.6loge(creatinine [mg/dL]) + 6.4(etiology: 0 if cholestatic or alcoholic, 1 otherwise).

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