A multicenter study of altered level of consciousness in the emergency room.

New-onset altered level of consciousness (ALC) is a challenge in real-world clinical practice. Although its presentation is nonspecific and its etiology is intricate, the term ALC is frequently used in the emergency room (ER). This study aimed to clarify and classify the etiologies and outcomes of the ALC in the ER. We retrospectively investigated ALC patients in the ER of four tertiary referral centers from February 2018 to January 2020. The etiology of ALC was comprehensively analyzed by a consortium of university professors, board-certified clinicians in neurology, emergency medicine, or internal medicine. The time point to determine the etiology of ALC was at the time of discharge from the ER. A total of 315,526 patients who visited ER due to ALC were reviewed and found 7988 eligible patients, of which 4298 (53.8%) were male and 5282 (66.1%) were older than 60. The overall mortality was 13.5%. Except undetermined, the 9 etiologies (n = 7552) were categorized into extra- (n = 4768, 63.1%) or intracranial etiology (n = 2784, 36.9%). The most common etiology of ALC in the ER was metabolic cause (n = 1972, 24.7%), followed by systemic infection (n = 1378, 17.3%). The majority of ALC in the ER was derived from extracranial etiology. ALC in the ER is a neurological manifestation of diverse etiologies; not all can be confirmed in the ER. Not only neurological but also critical systemic illnesses should be considered to assess the protean manifestations of ALC in the ER.