Yellow Score: A Predictive Model for Acute Liver Failure in Yellow Fever

Between 2017 and 2018, Brazil experienced the largest yellow fever (YF) outbreak ever recorded in the national territory. Many cases progressed to acute liver failure (ALF), making liver transplantation a therapeutic option. The applicability of the King’s College Criteria (KCC) in YF-related ALF is still uncertain, as are prognostic factors for mortality in the disease. This study proposes a new formula to estimate the risk of death in patients with YF, called the YELLOW Score (Yellow Fever End-stage Liver and Organ Worsening Score), and compares its performance with that of the KCC. The YELLOW Score was developed based on data from 229 patients with confirmed YF and age over 18 years, hospitalized in a reference hospital in Minas Gerais, Brazil, between January 2017 and March 2018. Demographic data, in-hospital mortality, and laboratory tests performed within the first 24, 36, and 48 hours after admission were analyzed in order to estimate risk factors and probability of death. Logistic regression models were used to compare the predictive performance of the YELLOW Score with that of the KCC. Among the 229 patients analyzed, 197 (86%) were male, with a median age of 46 years. The median time between symptom onset and hospitalization was four days (range: 0–40 days). Bleeding was reported in 41 patients (17.9%). Transfusions were administered to 64 patients (27.9%), while 26 (11.4%) required dialysis. Variables most strongly associated with mortality were considered for multivariate analysis. The final model included: age, oxaloacetic transaminase (AST), creatinine, direct bilirubin, and serum lactate. The AUROCs of the YELLOW Score models at 24h, 36h, and 48h were 0.89 CI 0.83–0.95, 0.88 CI 0.82–0.94, and 0.85 CI 0.78–0.92, respectively. Models based on the KCC showed AUROCs of 0.65 CI 0.56–0.74, 0.70 CI 0.61–0.79, and 0.64 CI 0.55–0.73. Analysis of these data suggests that the YELLOW model may outperform the KCC score in predicting mortality in this sample. Thus, although the effectiveness of liver transplantation in ALF caused by arboviruses is still debated, the YELLOW Score may be a useful tool in evaluating patients who are transplant candidates or for other interventions, such as plasmapheresis.