Nikkinen O, Jämsä E, Aaltonen T, et al. - Researchers analyzed primary elective hip and knee and emergency hip arthroplasty patients in this retrospective, register‐based study to assess the occurrence as well as the perioperative risk factors of acute kidney injury (AKI) in them. Also, the impact of urine output was assessed as a diagnostic criterion in addition to serum creatinine (sCr) concentrations. Participants were 731 patients who had primary elective knee or hip arthroplasty and 170 patients who had emergency hip arthroplasty between January 2016 and February 2017 in Finland. An elevated risk of AKI was observed in relation to emergency hip arthroplasty. Because an increase in mortality in both elective and emergency arthroplasty was brought about by AKI, perioperative oliguria is recommended to be also considered as a diagnostic criterion for AKI. Many cases of AKI may be overlooked if the focus is solely on sCr.