The relationship of multimorbidity with disability and frailty in the oldest patients: a cross-sectional analysis of three measures of multimorbidity in the BELFRAIL cohort.

BACKGROUND: Ageing people show increasing morbidity, dependence and vulnerability.
OBJECTIVES: To compare the relationships of different measures of multimorbidity with dependence (operationalized as disability) and vulnerability (operationalized as frailty).
METHOD: A cross-sectional analysis within the BELFRAIL cohort (567 subjects aged ≥ 80). Multimorbidity was measured using a disease count (DC), the Charlson comorbidity index (CCI) and the cumulative illness rating scale (CIRS), respectively. Associations with disability (based on activities of daily living) and frailty (defined by the Fried frailty criteria) were assessed using bivariable and multivariable analyses. Net reclassification improvement (NRI) values were calculated to compare the abilities of the DC, CCI and CIRS to identify patients with disability or frailty.
RESULTS: Disability was associated with the DC (crude odds ratio, OR: 2.1; 95% confidence interval, CI: 1.4-3.4), CCI (crude OR: 1.8; 95% CI: 1.2-2.7) and CIRS (crude OR: 4.0; 95% CI: 2.5-6.5); only the association with CIRS was independent of age, sex, chronic inflammation, impaired cognition and frailty (adjusted OR: 3.2; 95% CI: 1.7-5.8). Frailty was associated with CCI (crude OR: 2.4; 95% CI: 1.2-4.6) and CIRS (crude OR: 2.6; 95% CI: 1.3-5.3); adjusted for age, sex, chronic inflammation, impaired cognition and disability. These associations were not statistically significant. The NRIs demonstrated a similar ability of the DC, CCI, and CIRS to identify patients with disability or frailty, respectively.
CONCLUSION: The associations of different measures of multimorbidity with disability and frailty differ but their ability to identify patients with disability or frailty is similar. Generally, multimorbidity scores incompletely reflect dependence and vulnerability in this age group.