Development and calibration of a simple mortality risk score for hospitalized COVID-19 adults

Objectives Mortality risk scores, such as SOFA, qSOFA, and CURB-65, are quick, effective tools for communicating a patient’s prognosis and guiding therapeutic decisions. Most use simple calculations that can be performed by hand. While several COVID-19 specific risk scores exist, they lack the ease of use of these simpler scores. The objectives of this study were (1) to design, validate, and calibrate a simple, easy-to-use mortality risk score for COVID-19 patients and (2) to recalibrate SOFA, qSOFA, and CURB-65 in a hospitalized COVID-19 population. Design Retrospective cohort study incorporating demographic, clinical, laboratory, and admissions data from electronic health records. Setting Multi-hospital health system in New York City. Five hospitals were included: one quaternary care facility, one tertiary care facility, and three community hospitals. Participants Patients (n=4840) with laboratory-confirmed SARS-CoV2 infection who were admitted between March 1 and April 28, 2020. Main outcome measures Gray’s K-sample test for the cumulative incidence of a competing risk was used to assess and rank 48 different variables’ associations with mortality. Candidate variables were added to the composite score using DeLong’s test to evaluate their effect on predictive performance (AUC) of in-hospital mortality. Final AUCs for the new score, SOFA, qSOFA, and CURB-65 were assessed on an independent test set. Results Of 48 variables investigated, 36 (75%) displayed significant (p<0.05 by Gray’s test) associations with mortality. The variables selected for the final score were (1) oxygen support level, (2) troponin, (3) blood urea nitrogen, (4) lymphocyte percentage, (5) Glasgow Coma Score, and (6) age. The new score, COBALT, outperforms SOFA, qSOFA, and CURB-65 at predicting mortality in this COVID-19 population: AUCs for initial, maximum, and mean COBALT scores were 0.81, 0.91, and 0.92, compared to 0.77, 0.87, and 0.87 for SOFA. We provide COVID-19 specific mortality estimates at all score levels for COBALT, SOFA, qSOFA, and CURB-65. Conclusions The COBALT score provides a simple way to estimate mortality risk in hospitalized COVID-19 patients with superior performance to SOFA and other scores currently in widespread use. Evaluation of SOFA, qSOFA, and CURB-65 in this population highlights the importance of recalibrating mortality risk scores when they are used under novel conditions, such as the COVID-19 pandemic. This study’s approach to score design could also be applied in other contexts to create simple, practical and high-performing mortality risk scores. Trial registration NA Funding source The authors declare that there was no external funding provided. What is already known on this topic What this study adds ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The authors declare that there was no external funding provided for this study. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Mount Sinai Institutional Review Board (IRB-20-03613) All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Any secondary use of study data is contingent upon approval by the Mount Sinai Data Use Committee. Please contact the corresponding author for further information.