Measurements

Clinical data including demographics, blood test results including serum creatinine and eGFR at the time of ED presentation and at the time of the last measurement between 7 days and 1 year before the ED encounter (baseline), initial vital signs (systolic blood pressure, body temperature, and level of consciousness) in ED, chief complaints about ED visit, and important medical conditions such as sepsis, types of infections, and abnormal body temperature were extracted from the electronic medical record and were reviewed by two emergency physicians. Body mass index was also recorded when available. Altered mental status (AMS) was defined as a Glasgow Coma Scale lower than 15. For both of ED and baseline values, serum creatinine levels were measured at the central laboratory of our hospital by enzymatic method with LABOSPECT 008α (Hitachi High-Tech^®, reference ranges: 0.65–1.07 mg/dL for male and 0.46–0.79 mg/dL for female). The Modified Diet Renal Disease equation for Japanese patients [31] was used for eGFR calculation. Referring to the Sequential Organ Failure Assessment (SOFA) score [32], known predictors of poor clinical outcomes (platelet counts and total bilirubin levels on the day of ED visit) were also collected. For all patients, clinical outcomes, including hospitalization, hospital death, need of ICU treatment, and RRT, were recorded.

The patient’s renal dysfunction was categorized into the following: “AKI only,” “CKD only,” “AKI on CKD,” “subclinical kidney injury,” or “undetermined renal dysfunction (URD).” Patients who had baseline data for their renal function were assessed for the presence of AKI or CKD. AKI and CKD were diagnosed based on the criteria shown in the KDIGO guidelines [24, 25]. AKI was diagnosed when a patient’s ED creatinine had increased from the baseline by greater than 0.3 mg/dL or 50%. CKD was diagnosed when a patient had a baseline eGFR lower than 60 mL/min/1.73m². “AKI on CKD” was diagnosed when a patient simultaneously met the criteria for AKI and CKD. When a patient did not have 0.3 mg/dL or 50% increase of serum creatinine from the baseline, and the baseline eGFR was greater than 60 mL/min/1.73m², that patient did not meet the criteria for any of AKI and CKD. Such patients were categorized into the “subclinical kidney injury” because the eGFR at ED visit was below 60 mL/min/1.73m². Those who had no data of baseline renal function were coded as “URD.”