Regular article Screening for serious mental illness in populations with co-occurring substance use disorders: Performance of the K6 scale James A. Swartz, (Ph.D.) a, 4 , Arthur J. Lurigio, (Ph.D.) b a Jane Addams College of Social Work, University of Illinois at Chicago, Chicago, IL 60607, USA b College of Arts and Sciences, Loyola University Chicago, Chicago, IL 60626, USA Received 9 December 2005; accepted 23 April 2006 Abstract Serious mental illnesses (SMIs) such as schizophrenia, bipolar disorder, and major depression are prevalent among individuals with substance use disorders, particularly those in drug treatment programs. No screening tool has yet become the gold standard for identifying SMI among individuals with substance use disorders. One candidate instrument, the K6 screening scale, is brief, easy to administer and score, and has performed well, detecting SMI in studies using general population samples. We used data from the National Survey on Drug Use and Health to examine the K6’s psychometric properties in a subsample of persons with substance use disorders and found that the K6 accurately screened for severe psychological distress associated with SMI among individuals with substance use disorders and across different psychiatric disorders. D 2006 Elsevier Inc. All rights reserved. Keywords: Screening; Serious mental illness; Co-occurring disorders; Addiction 1. Introduction Substance use disorders are the most prevalent and clinically severe disorders affecting persons with serious mental illness (SMI), such as major depression, bipolar disorder, and schizophrenia (Blanchard, Brown, Horan, & Sherwood, 2000; Chambers, Krystal, & Self, 2000; Negrete, 2003; Substance Abuse and Mental Health Services Admin- istration [SAMSHA], 2005; Swendsen & Merikangas, 2000; Trull, Sher, Minks-Brown, Durbin, & Burr, 2000). Co- occurring or comorbid disorders refer to the presence of one or more psychiatric or substance use disorders in the same person, at the same time (Strakowsi & DelBello, 2000). Co-occurring disorders are common in the general popula- tion, afflicting millions of adults in the United States (SAMHSA, 2002). The National Survey on Drug Use and Health (NSDUH) reported that 4 million adults met the diagnostic criteria for both SMI and substance abuse and dependence problems in 2002 (U.S. Department of Health and Human Services [DHHS], SAMHSA, Office of Applied Studies [OAS], 2004). Depending on the sampling procedures, definitions of disorders, and assessment tools used in various studies of comorbidity, 20% to 65% of persons with SMI also had a lifetime substance use disorder (Mueser, Noordsy, Drake, & Fox, 2003). In the Epidemiological Catchment Area Study, for example, which included more than 20,000 randomly selected persons who participated in structured psychiatric interviews, nearly half of the adults diagnosed with schizophrenia (48%) and more than half of those diagnosed with bipolar disorder (56%) had one or more substance use disorders (Regier et al., 1990). More recently, in the National Comorbidity Survey Replication Study, which involved a representative sample of more than 9,000 adults, Kessler, Chiu, Demler, and Walters (2005) found that 45% of the participants met the criteria for two or more diagnoses, a considerable proportion of whom had com- binations of psychiatric and substance use disorders 0740-5472/06/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jsat.2006.04.009 4 Corresponding author. Tel.: +1 312 996 8560; fax: +1 312 996 2770. E-mail address: jaswartz@uic.edu (J.A. Swartz). Journal of Substance Abuse Treatment 31 (2006) 287 – 296