Comorbidity indices in observational studies on cardiovascular risk

To analyse comorbidity measures in relation to cardiovascular disease risk, using data from Swedish healthcare registries. The aim was to evaluate the performance of different indices in predicting incidences of four outcomes: coronary heart disease (CHD), myocardial infarction (MI), heart failure (HF) and stroke.

Study population: All individuals in Sweden born between 1936 and 1975, with a look-back for diagnosis data 2010-2014 and followed-up for outcomes from 2024 to 2019, n=4 454 895 individuals. Two age groups: 40-64 and 65-79 years old were studied. We used the area under the receiver operating characteristic curves (AUROC) of age-and-sex, the Nordic Multimorbidity Index (NMI), a set of five cardiovascular risk factors as indicator variables (CV-IV) and explored measures based on inpatient care and numbers of filled prescriptions.

In the age group 40-64 years, the AUROCs for age-and-sex alone were higher than those for the indices alone in all analyses: CHD (0.739); MI (0.736); HF (0.730) and stroke (0.685). CV-IV alone showed a higher AUROC for HF (0.694; 95% CI 0.690 to 0.697) than that for NMI (0.643; 95% CI 0.639 to 0.647), and for numbers of filled prescriptions (0.671; 95% CI 0.667 to 0.675).Highest AUROC was observed for HF, when taking age-and-sex into account, for CV-IV (0.781; 95% CI 0.778 to 0.784) followed by numbers of filled prescriptions (0.776; 95% CI 0.773 to 0.780) and NMI (0.771; 95% CI 0.768 to 0.774). Furthermore, AUROC was higher for CV-IV, when taking age-and-sex into account, than that of age-and-sex alone for all outcomes in both age groups.

AUROC for age-and-sex alone was higher than that for any other single measure alone for all outcomes. The highest AUROC observed was for CV-IV adjusted for age-and-sex for HF. Thus, simple indicators measuring a few well-established cardiovascular risk factors outperformed a complex index such as the NMI. Similar results were obtained for numbers of filled prescriptions implying possible use as a proxy measure for comorbidity.