Introduction Kidneys are among the affected organs in COVID-19 and there may be different etiologies resulting in acute kidney injury (AKI) in different stages of the disease. This study aimed to analyze AKI among hospitalized COVID-19 patients in relation to the time and etiologies of AKI.Materials & Methods 1056 patients who were hospitalized with COVID-19 diagnosis in our institution were retrospectively evaluated and 383 of them met the inclusion criteria. Eighty-nine patients who developed

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... AKI were involved in the final analysis. As immunologic response is generally accepted to start with the second week of COVID-19 course, patients were classified into three groups, those who had AKI on admission, those who developed AKI in the first week and those who developed AKI starting from 7th day. Initial lymphocyte counts, creatinine levels and inflammatory markers as well as changes in these parameters were compared between the groups.Results AKI was seen in 23% of the patients and 23% of those who developed AKI died. Patients who developed AKI later had higher peak CRP and D-dimer levels with lower nadir lymphocyte counts (p=0,000, 0,004 and 0,003 respectively). Additionally, patients who died had higher initial inflammatory marker levels and lower lymphocyte counts than those who survived. Mortality of patients who had AKI on hospital admission (13%) was similar to the overall COVID-19 mortality for inpatients, however it was as high as 44% for those who developed AKI after 7th day.Conclusion Early AKI was more related to pre-renal causes and had a milder course. However, later AKIs were more related to immunologic response and had significantly higher mortality. Findings of this study suggest that AKI in COVID-19 is not of one kind. When developed, AKI should be evaluated in conjunction with the disease stage and possible etiologies.