Acute and chronic kidney disease and risk of hospital mortality during COVID-19 pandemic waves in the pre-vaccination era

Background Chronic kidney disease (CKD) is a risk factor for death from coronavirus disease 2019 (COVID-19), and COVID-19 may cause acute kidney injury (AKI) which also influences outcomes. There is little information on the independent contribution of CKD and AKI to the risk of death in COVID-19 on different waves, as CKD is a key risk factor for AKI. Methods We have studied the epidemiology of CKD and AKI in 2878 patients hospitalized for COVID-19 and their independent association with in-hospital mortality in the two largest pre-vaccination COVID-19 waves in Madrid, Spain. Hospitalized COVID-19 patients were grouped into four mutually exclusive categories: previous-CKD, community-acquired AKI (CA-AKI), hospital-acquired AKI (HA-AKI) and normal renal function throughout hospitalization. Results Pre-existent or acquired kidney involvement was observed in 35.5% and 36.8% of COVID-19 patients in the 1st and 3rd waves, respectively. Overall, 13.9% of patients with normal kidney function on arrival developed HA-AKI. In the 3rd wave, CA-AKI was more common than in the 1st wave. Overall, 9%-20% of CKD cases and 22%-40% of AKI cases remained undiagnosed in the discharge report. CKD, CA-AKI and HA-AKI were independently associated with risk of death in multivariate analysis, with HA-AKI, which was usually mild, being the most relevant independent risk factor for in-hospital mortality. A model including kidney involvement category, age, Charlson index, admission lactate dehydrogenase and lymphocytes predicted death with a receiver operating characteristic area under the curve of 0.898. Conclusion In conclusion, CKD and AKI were common in pre-vaccination waves among hospitalized COVID-19 patients and were independent risk factors for death, even when AKI was mild to moderate, and despite improvements in treatment.