New Multimorbidity Score Better Than Charlson Comorbidity Index?

Troy Brown, RN

February 03, 2020

A new multimorbidity score is better at quantifying multiple chronic health conditions than the currently used Charlson Comorbidity Index, researchers say.

"This tool will be of use to people involved in planning health services and for deciding who should potentially be prioritized for tailored multimorbidity care. It's not specifically designed for use with an individual patient ― rather, for deciding which patients within a particular population (for example, those people registered with a particular family practice) should be targeted with interventions designed to optimize care for multimorbidity," lead researcher Rupert Payne, MBChB, PhD, told Medscape Medical News.

Payne, from the Center for Academic Primary Care, University of Bristol, United Kingdom, and colleagues report their findings in an article published onlined today in CMAJ.

They modeled the association between 37 morbidities and primary care consultations, unplanned hospital admission, and mortality at 1 and 5 years. Some of the conditions that were included in the model are hypertension, anxiety/depression, painful condition, hearing loss, irritable bowel syndrome, asthma, diabetes mellitus, coronary heart disease, and chronic kidney disease.

"[T]he aim of our study was to develop not the best risk prediction tools, but rather an optimal approach to describe or adjust for the general health status of individuals in health services and outcomes research," the authors write.

The researchers used 300,000 samples from the UK Clinical Practice Research Datalink for development and 150,000 samples for validation. They averaged the standardized weights of individual outcome scores to construct a general-outcome multimorbidity score and compared the performance of the Cambridge Multimorbidity Score with the Charlson Comorbidity Index, which was developed in the 1980s.

For the new multimorbidity score, models that used all 37 conditions adequately predicted general practitioner consultations (C-index, 0.732), unplanned hospital admission (C-index, 0.742), and mortality (C-index, 0.912) at 1 year.

Models that included only the 20 most important conditions with the highest combined prevalence/weight demonstrated similar predictive ability (C-indices, 0.727, 0.738, and 0.910, respectively).

At 5 years, results for consultations and death were similar (C-indices, 0.735 and 0.889, respectively) but were lower for admissions (C-index, 0.708).

When the researchers averaged the standardized weights of the individual outcome scores to construct a general-outcome multimorbidity score, the general-outcome multimorbidity score performed similarly to the outcome-specific models. Performance was significantly better than models based on the Charlson Comorbidity Index for consultations (C-index, 0.691) and admissions (C-index, 0.703) but was similar for mortality (C-index, 0.907).

Charlson Comorbidity Index Has Limitations

It's not that the Charlson Comorbidity Index is failing, Robert McLean, MD, MACP, practicing internist and rheumatologist in New Haven, Connecticut, with the Northeast Medical Group of Yale New Haven Health, told Medscape Medical News.

"[M]uch of the early work with the Charlson Comorbidity Index was done in oncology patients, and so some might think it has not been validated as extensively in non-oncologic patients and populations," continued McLean, an associate clinical professor of medicine at Yale School of Medicine.

Medical practice has advanced considerably since the Charlson was developed, Payne told Medscape Medical News. As a result, the high weighting given to some disorders in the Charlson index may no longer be as appropriate. For example, patients with HIV currently have a "near-normal life expectancy due to advances in antiviral therapy," he said.

"Charlson also considers a smaller number of health problems than the Cambridge Multimorbidity Score, so although a patient may have several long-term conditions, these may not correspond to those on the Charlson list (but may be captured by the Cambridge list)," Payne continued.

"Finally, the different conditions used to calculate the Charlson score are weighted based on the risk of death that they each carry," said Payne. "That's important if you want to know the impact of multimorbidity on risk of dying, but may not necessarily be relevant when considering the impact of multimorbidity on things like health service utilization ― as well as death; the Cambridge score allows users to examine the impact of multimorbidity on primary care service use and unplanned hospitalization. It also provides an 'average' score too (based on an average of death, hospitalization, and primary care use)."

Next Steps

It is possible to use the Cambridge score in practice; however, others will surely wish to study it further, "such as in specific patient groups or in different health service settings," Payne said. "In addition, different health systems use different approaches to coding clinical data. Our study used the UK Read code system, but countries using other systems, such as SNOMED or ICD would need to translate the codes (although this in general would not be too difficult)."

McLean agreed on the benefit of additional research. "In clinical medicine, we tend to not like to make significant changes in practice or testing patterns based on a single study. Clinical and biological systems are complex, and it is difficult to account for every variable that can affect a study's outcome or reliability. Therefore, clinicians like to see follow-up studies confirming results," he said.

"We have described the development of several robust, simple-to-use multimorbidity scores, some tailored and others not tailored to specific health and health service outcomes. These scores have the potential to be of considerable value for policy development and clinical priority-setting, providing a clinically relevant, pragmatic, transparent and methodologically easy-to-implement means of optimizing the delivery of health care to an aging and increasingly multimorbid population," the researchers conclude.

The authors and McLean have disclosed no relevant financial relationships.

CMAJ. Published online February 3, 2020. Full text

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