See related editorial by Kennedy et al. in this issueOBJECTIVE: To examine the ability of the family-rated Family Confusion Assessment Method (FAM-CAM) to identify delirium in the emergency department (ED) among patients with and without dementia, as compared to the reference-standard Confusion Assessment Method (CAM). DESIGN: Validation study. SETTING: Urban academic ED. PARTICIPANTS: Dyads of ED patients, aged 70 years and older, and their family caregivers (N = 108 dyads). MEASUREMENTS: A trained reference standard interviewer performed a cognitive screen, delirium symptom assessment, and scored the CAM. The caregiver self-administered the FAM-CAM. Dementia was assessed using the Informant Questionnaire on Cognitive Decline in the Elderly and the medical record. For concurrent validity, performance of the FAM-CAM was compared to the CAM. For predictive validity, clinical outcomes (ED visits, hospitalization, and mortality) over 6 months were compared in FAM-CAM positive and negative patients, controlling for age, sex, comorbidity, and cognitive status. RESULTS: Among the 108 patients, 30 (28%) were CAM positive for delirium and 58 (54%) presented with dementia. The FAM-CAM had a specificity of 83% and a negative predictive value of 83%. Most false negatives (n = 9 of 13, 69%) were due to caregivers not identifying the inattention criteria for delirium on the FAM-CAM. In patients with dementia, sensitivity was higher than in patients without (61% vs 43%). In adjusted models, a hospitalization in the following 6 months was more than three times as likely in FAM-CAM positive compared to negative patients (odds ratio = 3.4; 95% confidence interval = 1.2-9.3). CONCLUSIONS: Among patients with and without dementia, the FAM-CAM shows qualities that are important in the ED setting for identification of delirium. Using the FAM-CAM as part of a systematic screening strategy for the ED, in which familiesʼ assessments could supplement healthcare professionalsʼ assessments, is promising. J Am Geriatr Soc 00:983-990, 2020. D elirium, an acute decline in cognitive function, is common among hospitalized older patients and is associated with poor clinical and functional outcomes. 1 The emergency department (ED) is the point of hospital entry for the vast majority of inpatients, and up to 20% of older patients in the ED have prevalent delirium. 2 Patients with delirium in the ED are at risk for poor outcomes, including longer and more complicated hospital stays, slower functional recovery, and readmission. 3 More important, patients discharged home with delirium have a high mortality rate. 4 Despite its high prevalence, delirium often goes undiagnosed in the ED, even though it is included in quality indicators, emergency medicine resident core competencies, and guidelines. 2,[5][6][7][8] In the context of the ED, identifying delirium is a primary concern; and since longer duration of delirium is associated with poorer outcomes, early identification is key. 3,4 Moreover, many older patients in the ED have dementia, which is a le...