External Validation of the ImAgeS Risk Score for Mortality in Hospitalized Kidney Transplant Recipients with COVID-19: A Retrospective Observational Study

Background: Timely recognition of high-risk individuals with novel Coronavirus disease (COVID-19) is important. Yet, validated risk scores for kidney transplant recipients with COVID-19 are lacking. The present study aimed to externally validate the novel ImAgeS risk score in this population. Methods: A retrospective analysis of 65 kidney transplant recipients with COVID-19 was conducted. A robust external validation of the novel ImAgeS risk score with respect to 30-day all-cause mortality was performed using regression analysis, discrimination and calibration methods. Results: An overall mortality rate during the study follow-up was 18.5% (N = 12). The ImAgeS risk score showed a statistically significant association with 30-day all-cause mortality (HR 1.04 95% CI 1.00–1.08, p =  0.040). This risk score demonstrated a modest, statistically significant discrimination of all-cause mortality (AUC of 0.679 (95% CI 0.519–0.840, p = 0.027). The calibration of the model was acceptable with a Hosmer-Lemeshow value of 3.74, Harrell’s C concordance index of 0.699 and Somers’ D of 0.397. Conclusions: The ImAgeS risk score demonstrated a significant association with 30-day all-cause mortality in kidney transplant recipients with COVID-19. The model showed modest discrimination and satisfactory calibration, confirming the findings from the computational study. Further studies are needed to determine the utility of the ImAgeS score in this high-risk population.