Background
Identifying predictive factors for coronavirus disease 2019 (COVID-19) is crucial for risk stratification and intervention. Kidney dysfunction contributes to the severity of various infectious diseases. However, the association between on-admission kidney dysfunction and the clinical outcome in COVID-19 patients is unclear.

Methods
This study was a multicenter retrospective observational cohort study of COVID-19 patients, diagnosed by polymerase chain reaction. We retrospectively analyzed 500 COVID-19 patients (mean age: 51 ± 19 years) admitted to eight hospitals in Japan. Kidney dysfunction was defined as a reduced estimated glomerular filtration rate (< 60 mL/min/1.73 m2) or proteinuria (≥ 1 + dipstick proteinuria) on admission. The primary composite outcome included in-hospital death, extracorporeal membrane oxygenation, mechanical ventilation (invasive and noninvasive methods), and intensive care unit (ICU) admission.

Results
Overall, 171 (34.2%) patients presented with on-admission kidney dysfunction, and the primary composite outcome was observed in 60 (12.0%) patients. Patients with kidney dysfunction showed higher rates of in-hospital death (12.3 vs. 1.2%), mechanical ventilation (13.5 vs. 4.0%), and ICU admission (18.1 vs. 5.2%) than those without it. Categorical and multivariate regression analyses revealed that kidney dysfunction was substantially associated with the primary composite outcome. Thus, on-admission kidney dysfunction was common in COVID-19 patients. Furthermore, it correlated significantly and positively with COVID-19 severity and mortality.

Conclusions
On-admission kidney dysfunction was associated with disease severity and poor short-term prognosis in patients with COVID-19. Thus, on-admission kidney dysfunction has the potential to stratify risks in COVID-19 patients.