Validity of medication-based co-morbidity indices in the Australian elderly population.
OBJECTIVE
To determine the validity of two medication-based co-morbidity indices, the Medicines Disease Burden Index (MDBI) and Rx-Risk-V in the Australian elderly population.


METHODS
In Phase I, the sensitivity and specificity of both indices were determined in 767 respondents from wave 6 of the Australian Longitudinal Study of Ageing (ALSA). Medication-defined index disease categories were compared to self-reported medical conditions. Correlation with self-rated health was examined and Cox proportional hazards models were used to assess the predictive validity for mortality. Phase II verified the predictive ability of Rx-Risk-V in a sample of 213,191 veterans from Australian Department of Veterans' Affairs (DVA) database.


RESULTS
MDBI and Rx-Risk-V scores could be calculated for 28% and 73% of the ALSA sample respectively. Both indices had high specificities and low to moderate sensitivities compared to self-reported medical conditions. Total weighted scores were significantly related to self-rated health (p<0.001). Both indices were predictive of mortality (Hazard Ratio (HR) =3.690 (95% CI 2.264-6.015) for MDBI and HR 1.079 (95% CI 1.045-1.114) for Rx-Risk-V. The predictive validity for mortality of Rx-Risk-V was confirmed using DVA data (HR= 1.090, 95% CI 1.088-1.092).


CONCLUSIONS
Medication-based co-morbidity indices Rx-Risk-V and MDBI are valid measures of co-morbidity. However, Rx-Risk-V detects more comorbidity in the Australian elderly population and is likely to be a more suitable index to use in administrative datasets, particularly where studies include large numbers of outpatients.
Sansom Institute, University of South Australia, Adelaide, Australia. Agnes.Vitry@unisa.edu.au
Agnes
A
Vitry
Soo Ann
SA
Wong
Elizabeth E
EE
Roughead
Emmae
E
Ramsay
John
J
Barratt
D000368:Aged; D000369:Aged, 80 and over; D001315:Australia / Q000453:epidemiology; D015897:Comorbidity; D004363:Drug Utilization; D006305:Health Status Indicators; D006801:Humans; D008137:Longitudinal Studies; D009026:Mortality; D055553:Prescription Drugs / Q000627:therapeutic use*; D016016:Proportional Hazards Models; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires / Q000592:standards*; D014728:Veterans
D055553:Prescription Drugs