The measurement of multiple chronic diseases--a systematic review on existing multimorbidity indices

Multimorbidity, defined as the coexistence of 2 or more chronic diseases, is a common phenomenon especially in older people. Numerous efforts to establish a standardized instrument to assess the level of multimorbidity have failed until now, and indices are primarily characterized by their high heterogeneity. Thus, the objective is to provide a comprehensive overview on existing instruments on the basis of a systematic literature review.

The review was performed in MedLine. All articles published between January 1, 1960 and August 31, 2009 in German or English language, with the primary focus either on the development of a weighted index or on the effect of multimorbidity on different outcomes, were identified.

A total of 39 articles met the inclusion criteria. In the majority of studies (59.0%), the list of included diseases was presented without any selection criteria. Only the high prevalence of diseases (17.9%), their impact on mortality, function, and health status served as a point of reference. Information on the prevalence of chronic conditions mostly rely on self-reports. On average, the 39 indices included 18.5 diseases, ranging between 4 and 102 different conditions. Most frequently mentioned diseases were diabetes mellitus (in 97.5% of indices), followed by stroke (89.7%), hypertension, and cancer (each 84.6%). Overall, three different weighting methods could be distinguished.

The systematic literature further emphasis the heterogeneity of existing multimorbidity indices. However, one important similarity is that the focus is on diseases with a high prevalence and a severe impact on affected individuals.