BRIEF REPORT Design and Validation of a Methodology Using the International Classification of Diseases, 9th Revision, to Identify Secondary Conditions in People With Disabilities Leighton Chan, MD, MPH, Anne Shumway-Cook, PhD, Kathryn M. Yorkston, PhD, Marcia A. Ciol, PhD, Brian J. Dudgeon, PhD, Jeanne M. Hoffman, PhD ABSTRACT. Chan L, Shumway-Cook A, Yorkston KM, Ciol MA, Dudgeon BJ, Hoffman JM. Design and validation of a methodology using the International Classification of Dis- eases, 9th Revision, to identify secondary conditions in people with disabilities. Arch Phys Med Rehabil 2005;86:1065-9. Objective: To design and validate a methodology that iden- tifies secondary conditions using International Classification of Disease, 9th Revision (ICD-9) codes. Design: Secondary conditions were identified through a literature search and a survey of Washington State physiatrists. These conditions were translated into ICD-9 codes and this list was then validated against a national sample of Medicare survey respondents with differing levels of mobility and activ- ities of daily living (ADL) disability. Setting: National survey. Participants: Participants (N=9731) in the 1999 Medicare Current Beneficiary Survey with no, mild, moderate, and se- vere mobility and ADL disability. Interventions: Not applicable. Main Outcome Measure: Percentage of survey respondents with a secondary condition. The secondary conditions were grouped into 4 categories: medical, psychosocial, musculoskel- etal, and dysphagia related (problems associated with difficulty in swallowing). Results: Our literature search and survey of 26 physiatrists identified 64 secondary conditions, including depression, de- cubitus ulcers, and deconditioning. Overall, 70.4% of all sur- vey respondents were treated for a secondary condition. We found a significant relation between increasing mobility as well as ADL disability and increasing numbers of secondary con- ditions ( 2 test for trend, P.001). This relation existed for all categories of secondary conditions: medical ( 2 test for trend, P.001), psychosocial ( 2 test for trend, P.001), musculo- skeletal ( 2 test for trend, P.001), and dysphagia related ( 2 test for trend, P.001). Conclusions: We created a valid ICD-9 – based methodol- ogy that identified secondary conditions in Medicare survey respondents and discriminated between people with different degrees of disability. This methodology will be useful for health services researchers who study the frequency and impact of secondary conditions. Key Words: Disability evaluation; International Classifica- tion of Diseases; Medicare; Rehabilitation. © 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation R ESEARCH EXAMINING OUTCOMES in people with disability has led to an awareness of the importance of secondary conditions to health. 1 The issue first surfaced in 1988 in an article by Marge 2 in which he suggested that the health status of a person with a disability reflected not only the primary disabling conditions but also additional “secondary disabilities.” In 1991, the Institute of Medicine (IOM) 3 formal- ized the term “secondary conditions,” defining them as pre- ventable health conditions, such as decubitus ulcers and de- pression, that may develop in people with a primary disability. Although there is no consensus definition of a secondary con- dition, we used the IOM definition for this project. The few epidemiologic studies published on this subject suggest that secondary conditions are common among people with disabilities. 4-8 Researchers at the Massachusetts Depart- ment of Public Health developed a survey in 1995 to explore secondary conditions in 656 adults with major disabilities. 9 On average, respondents reported 5 secondary conditions (range, 0 –15), with 95% reporting having at least 1. The 5 most common secondary conditions were fatigue, depression, spasms, chronic pain, and anxiety. Mobility difficulties were associated with an increased number of secondary conditions. Identifying secondary conditions is difficult in large popu- lations. To date, most of the population-based studies have been small and have relied on patient recall to determine the prevalence of such conditions. Encounter, or billing, data are widely available and could allow assessment of secondary conditions in much larger populations than have been analyzed to date. 10 Because nearly every large billing database used codes from the International Classification of Disease, 9th Revision (ICD-9), we created an ICD-9 – based methodology to identify secondary conditions. We then tested the construct validity of this methodology in a national sample of Medicare survey respondents with differing levels of mobility and activ- ities of daily living (ADL) disability. METHODS This project took place in 2 stages. First, potential secondary conditions were identified and then translated into ICD-9 codes. In the second stage, construct validity of the codes was assessed. We searched PubMed, using the term preventable secondary conditions. Thirty articles were reviewed and 25 separate sec- ondary conditions were identified. We then presented these conditions to a listserve of 167 physiatrists for their feedback. From the Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, WA. Supported by the Centers for Disease Control and Prevention (grant no. MM-0625- 04/04) through a Potential Extramural Project Grant with the Association of Aca- demic Medical Centers, and the Centers for Medicare and Medicaid Services. No commercial party having direct financial interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated. Correspondence to Leighton Chan, MD, MPH, Dept of Rehabilitation Medicine, University of Washington, Box 356490, Seattle, WA 98195-6490, e-mail leighton@u.washington.edu. Reprints are not available from the author. 0003-9993/05/8605-9541$30.00/0 doi:10.1016/j.apmr.2004.11.011 1065 Arch Phys Med Rehabil Vol 86, May 2005