By Martin Fortin

Published data on chronic diseases and multimorbidity prevalence are mainly based on self-report, billing data and registries. Data, so far, show a large gap in their magnitude from one study to the other. Population-based data and primary care practice data show important discrepancies (1). Studies from several countries (2-4) used administrative data, but much variation in results is attributed to different conceptualizations of multimorbidity and various chronic disease definitions and classifications (5). The use of a validated measure or index appears promising but so far, no instrument has been formally identified for measuring multimorbidity and the resulting burden of disease either for the patient or at the practice level (6). Such an instrument would be a major contribution to the study of multimorbidity and for comparison purposes among practices, regions and countries. Resource allocation and policy making would also benefit from a robust measure that could be scored in various ways including the use of Electronic Medical Record (EMR) data.

We validated and used the Cumulative Illness Rating Scale (CIRS) in previous studies for the measure of multimorbidity using chart review (7-10).  Advantages were its exhaustive quality and the built-in assessment of severity. We have shown it to be a better predictor of health related quality of life (HRQoL) and psychological distress than the simple count of chronic diseases and it compared advantageously with other morbidity indexes when HRQoL was the outcome of interest (11-13). Others have used the count of CIRS domains as a measure of multimorbidity and have linked the domain to International Classification of Primary Care (ICPC) rubrics thus facilitating the link with EMR (14). We have shown that some domains of the CIRS did not correlate with outcomes for patients. Based on previous studies on multimorbidity (7-9, 12, 14-15) and our experience with the use of the CIRS, we developed the Multimorbidity Assessment Tool (MAT) aimed at measuring the burden of disease at patient level and to reflect on the burden for practices. The tool builds on the CIRS structure but redefines the domains to facilitate scoring. We removed the domains that were not associated with HRQoL (15). We also added other domains that were deemed more appropriate. For each domain, the score may vary from 0 to 3 depending on the number of conditions affecting the domain and their severity. The tool may generate various continuous scores depending on its use. The tool will be assessed for reliability and validity and is expected to be available in 2012..

References
1. Fortin M, Hudon C, Haggerty J, van den Akker M, Almirall J. Prevalence estimates of multimorbidity: a comparative study of two sources. BMC Health Services Research, 2010;10:111.
2. van den Akker, M., et al., Multimorbidity in general practice: prevalence, incidence, and determinants of co-occurring chronic and recurrent diseases. J Clin Epidemiol, 1998. 51: p. 367-375.
3. Macleod, U., et al., Comorbidity and socioeconomic deprivation: an observational study of the prevalence of comorbidity in general practice. European Journal of General Practice, 2004. 10(1): p. 24-6.
4. Uijen AA, van de Lisdonk EH. Multimorbidity in primary care: prevalence and trend over the last 20 years. Eur J Gen Pract. 2008;14 Suppl 1:28-32.
5. Valderas JM, Starfield B, Sibbald B, Salisbury C, Roland M. Defining comorbidity: implications for understanding health and health services. Ann Fam Med. 2009 Jul-Aug;7(4):357-63.
6. van den Akker, M., et al., Problems in determining occurrence rates of multimorbidity. J Clin Epidemiol, 2001. 54: p. 675-9.
7. Hudon C, Fortin M, Vanasse A. Cumulative Illness Rating Scale was a reliable and valid index in the family practice context. J Clin Epidemiol. 2005;58:603-8.
8. Hudon C, Fortin M, Soubhi H. Abbreviated guidelines for scoring the Cumulative Illness Rating Scale (CIRS) in family practice. Disponible à : www.elsevier.com/locate/clinepi J Clin Epidemiol. 2007; 60 :212.e1-e3.
9.  Fortin M, Bravo G, Hudon C, Vanasse A, Lapointe L. Prevalence of multimorbidity among adults seen in family practice. Ann Fam Med. 2005;3:223-28.
10. Fortin M, Steenbakkers K, Hudon C, Poitras ME, Almirall J, van den Akker M. The electronic Cumulative Illness Rating Scale: a reliable and valid tool to assess multimorbidity in primary care. Journal of Evaluation in Clinical Practice. Published online June 25th, 2010.
11. Fortin M, Bravo G, Hudon C, Lapointe L, Dubois MF, Almirall J. Psychological distress and multimorbidity in primary care. Ann Fam Med. 2006;4:417-22.
12. Fortin M, Bravo G, Hudon C, Lapointe L, Almirall J, Dubois M-F, Vanasse A. Relationship between multimorbidity and health-related quality of life of patients in primary care. Quality of Life Research. 2006;15:83-91.
13. Fortin M, Hudon C, Dubois MF, Almirall J, Lapointe L, Soubhi H. Comparative assessment of three different indices of multimorbidity for studies on health-related quality of life. Health and Quality of Life Outcomes. 2005;3:74. Disponible à: http://www.hqlo.com/content/3/1/74/abstract.
14. Britt HC, Harrison CM, Miller GC, Knox SA. Prevalence and patterns of multimorbidity in Australia. Med J Aust. 2008. 189(2):72-7.
15.Fortin M, Dubois MF, Hudon C, Soubhi H, Almirall J. Multimorbidity and quality of life: a closer look. HQLO 2007; 5 :52.