Performance of the EQ-5D-5L plus respiratory bolt-on in the Birmingham chronic obstructive pulmonary disease cohort study

Objectives
A respiratory bolt-on dimension for the EQ-5D-5L has recently been developed and valued by the general public. This study aimed to validate the EQ-5D-5L plus respiratory dimension (EQ-5D-5L+R) in a large group of patients with chronic obstructive pulmonary disease (COPD).

Methods
Validation was undertaken with data from the Birmingham COPD Cohort Study, a longitudinal UK study of COPD primary care patients. Data on the EQ-5D-5L+R were collected from 1008 responding participants during a follow-up questionnaire in 2017 and combined with (previously collected) data on patient and disease characteristics. Descriptive and correlation analyses were performed on the EQ-5D-5L+R dimensions and utilities, in relation to COPD characteristics and compared with the EQ-5D-5L without respiratory dimension. Multivariate regression models were estimated to test whether regression coefficients of clinical characteristics differed between the EQ-5D-5L+R utility and the EQ-5D-5L utility.

Results
Correlation coefficients for the EQ-5D-5L+R utility with COPD parameters were slightly higher than the EQ-5D-5L utility. Both instruments displayed discriminant validity but analyses in clinical subgroups of patients showed larger absolute differences in utilities for the EQ-5D-5L+R. In the multivariate analyses, only the coefficient for the COPD Assessment Test score was higher for the model using the EQ-5D-5L+R utility as outcome.

Conclusions
This study showed that the addition of a respiratory domain to the EQ-5D-5L led to small improvements in the instrument’s performance. Comparability of the EQ-5D across diseases, currently considered one of its strengths, would have to be traded off against a modest improvement in utility difference when adding the respiratory dimension.