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Multimorbidity in Medicare Beneficiaries: Performance of an ICD-Coded Multimorbidity-Weighted Index
Melissa Y Wei1,2, David Ratz3, Kenneth J Mukamal4
1Division of General Medicine, University of Michigan, Ann Arbor, Michigan.
Objectives:
Most older adults have multimorbidity that impairs physical functioning, but it is difficult to quantify using claims data. We previously developed and validated a multimorbidity-weighted index (MWI) that embeds physical functioning through disease weightings. We mapped these conditions to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes and compared them with existing indices.
Design:
Population-based prospective cohort.
Setting:
Respondents to the 2006-2016 waves of the Health and Retirement Study (HRS) with linked Medicare claims data and continuous enrollment in 2006.
Participants:
Community-dwelling Medicare-eligible HRS participants (N = 9923; mean age = 75.5 ± 8.5 y).
Measurements:
Individuals were followed for future physical functioning (2006-2014) and mortality (2007-2016). MWI conditions were mapped to ICD-9-CM codes to produce an ICD-coded MWI (MWI-ICD). We compared MWI-ICD, simple disease count, Charlson, Elixhauser, and the health-related quality of life comorbidity index (HRQOL-CI) through distributions, hazard ratios for mortality, and relationships with future physical functioning.
Results:
MWI-ICD exhibited the broadest distribution and most unique values (5891). Left censoring was most pronounced for Charlson (34.3% score = 0) and Elixhauser (13.1% score = 0) vs MWI (5.0% score = 0). Hazard ratios and concordance (C)-statistics for mortality across extreme quartiles were similar for MWI-ICD, Elixhauser, and Charlson but lower for disease count and the HRQOL-CI. For physical functioning, MWI-ICD yielded the greatest contrast across extreme quartiles and overall coefficient of determination (R2 ).
Conclusion:
MWI-ICD was significantly associated with mortality and future physical functioning and comparable with established metrics for mortality prediction although not weighted to mortality. MWI-ICD successfully captures diseases accumulation and functioning in claims data. J Am Geriatr Soc 68:999-1006, 2020.
Insights
The Multimorbidity-Weighted Index (MWI-ICD) effectively captures disease accumulation and its impact on physical functioning in older adults using Medicare claims data. This new index shows strong associations with mortality and future physical function.
Area of Science:
- Gerontology
- Health Services Research
- Epidemiology
Background:
- Multimorbidity is prevalent in older adults, often impairing physical functioning.
- Quantifying multimorbidity's impact using administrative claims data presents challenges.
- Existing indices may not fully capture the complexity of disease burden and its effect on function.
Purpose of the Study:
- To develop and validate an ICD-coded Multimorbidity-Weighted Index (MWI-ICD) for use with claims data.
- To assess the MWI-ICD's performance in predicting mortality and future physical functioning.
- To compare the MWI-ICD with existing comorbidity indices.
Main Methods:
- A population-based prospective cohort study using Health and Retirement Study (HRS) participants linked with Medicare claims.
- Mapping MWI conditions to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes.
- Comparing MWI-ICD with simple disease count, Charlson, Elixhauser, and HRQOL-CI for distributions, mortality prediction, and physical functioning relationships.
Main Results:
- MWI-ICD demonstrated the broadest distribution and most unique values compared to other indices.
- Left censoring (score of 0) was lowest for MWI-ICD (5.0%) compared to Charlson (34.3%) and Elixhauser (13.1%).
- MWI-ICD showed comparable mortality prediction to Charlson and Elixhauser and the greatest contrast and explanatory power for physical functioning.
Conclusions:
- The MWI-ICD is a valuable tool for quantifying disease accumulation and its impact on physical functioning in claims data.
- MWI-ICD shows significant associations with mortality and future physical functioning.
- This index offers a robust method for assessing multimorbidity burden in older adult populations.
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