Development of the Birmingham Lung Improvement Studies (BLISS) prognostic score for COPD patients in primary care: data from the Birmingham COPD cohort
COPD patients in primary care have high rates of hospital admissions. Prognostic scores could be used to guide management of COPD patients and reduce risk of hospital admission, but existing scores do not perform well enough and are not used in practice. We aimed to develop a new prognostic score that was practical for use in the primary care setting.
Using data from the Birmingham COPD cohort we developed and internally validated the new BLISS prognostic score to predict respiratory admissions in 2-years from 23 candidate predictors. 1558 patients on COPD registers of 71 GP practices and 331 newly-identified patients from a linked case-finding trial were included and their self-reported and clinical data were combined with routine hospital episode statistics. The primary outcome was the record of at least one respiratory admission within 2 years of cohort entry (May 2012-June 2014). The model was developed using backward elimination of variables with p<0.157. Missing data were imputed using chained equations. Discrimination and calibration were assessed. Bootstrapping was used for internal validation, adjusting for overfitting and deriving optimum-adjusted performance statistics.
Median (min, max) follow up was 3.0 years (1.8, 3.8). Of the 23 candidate predictors, 6 variables were retained in the final model: age, CAT score, respiratory admissions in the previous 12m, BMI, diabetes, FEV1% predicted. After adjustment for optimism, the model showed promising discrimination in predicting risk of respiratory admissions by 2 years (c-statistic=0.73 (95%CI 0.70, 0.77). The BLISS score showed promising performance in predicting respiratory admissions compared with existing published scores.
All 6 variables are readily available in primary care records or would be easy to collect, and a simple computer programme could calculate the score. Important next steps are external validation in other settings, proposing and evaluating a model of use to guide patient management and exploration of the best ways to implement the score in primary care practice.