BACKGROUND AND HYPOTHESIS: Chronic kidney disease (CKD) is a major prognostic factor in COVID-19. Little is known about the significance of newly detected renal impairment (RI) for COVID-19 patient outcomes. This study assessed the effect of prior CKD and RI at admission on in-hospital mortality in COVID-19 patients. METHODS: A total of 5191 consecutive patients with COVID-19 admitted between March 6, 2020 and May 31, 2021, to the University Hospital in Krakow were analyzed. The main outcome was in-hospital death from any cause compared between the three study groups - patients with a prior history of CKD (group A), no history of CKD and eGFR on admission <
60 mL/min/1,73 m2 (group B), and no history of CKD and eGFR on admission >
60 mL/min/1,73 m2 (group C). RESULTS: Of 5191 patients, 2348 (45.2%) were women and 2409 (46.4%) were older than 65 years (mean age of 61.98±16.66 years). There were 483 (9.3%) patients in group A, 1009 (22.2%) in group B and 3699 (68.5%) in group C. Groups A and B were older and had higher cardiometabolic burden compared to group C. Multivariable logistic regression showed that older age, higher CRP, WBC, D-dimer levels, HF, and being in groups A or B were associated with higher in-hospital mortality. Group B had the highest risk (OR 3.003, CI 2.298-3.926) compared to group A (OR 2.020, CI 1.636-2.494) and group C (reference). CONCLUSION: COVID-19 patients with prior CKD and newly detected RI have higher odds of in-hospital death compared to those with normal kidney function. Special attention is needed for newly detected RI cases in COVID-19 patients.