ArticlesExpansion of the prognostic assessment of patients with chronic obstructive pulmonary disease: the updated BODE index and the ADO index
Introduction
The BODE index was an important contribution to prognostic research in chronic obstructive pulmonary disease (COPD).1 It combines information about several predictors including body-mass index (BMI), airflow obstruction (forced expiratory volume in 1 s [FEV1]), dyspnoea (Medical Research Council [MRC] dyspnoea scale), and exercise capacity (6-min walk distance) in a score ranging from 0 to 10. This prognostic index predicts mortality significantly better than does lung function—the traditional prognostic COPD indicator—alone. The BODE index contributed to the acceptance that prognostic assessment in patients with COPD should go beyond lung function.2, 3
Findings from several studies4, 5, 6 have confirmed that the BODE index has better discriminative properties than does lung function. Discrimination refers to the ability of the prognostic index to distinguish between patients who will or will not die over a specific period of time. However, discrimination is not the only property that is relevant for prognostic indices. To be useful in practice, prognostic instruments should accurately predict the absolute risk of an event in individual patients.7 Guided by these predicted risks, clinicians and patients might decide on more or less comprehensive treatment to modify that risk. The absolute risks as predicted by risk scores should be compared with the observed risks in at least one other population (so-called calibration).8, 9, 10 Without any assessment of calibration, clinicians should be very cautious in applying such scores in practice because treatment selection could be inadequate if the risk is overestimated or underestimated. Unlike widely used risk scores such as the Framingham risk score and the APACHE (acute physiology and chronic health evaluation) scores, the BODE index does not provide absolute risks of mortality and its calibration has never been assessed. As a consequence, the BODE index seems not yet ready for use as a prognostic instrument in patients with COPD.
We aimed to assess the calibration of the BODE index in two different COPD populations, to explore how its prediction could be improved, and to develop a simplified risk index that is also applicable in primary-care settings.
Section snippets
Study design and patients
We included all patients with COPD in the Swiss Barmelweid cohort and the Spanish Phenotype and Course of COPD (PAC-COPD) cohort study.11 Patients in the Swiss cohort had longstanding and, on average, severe COPD (according to criteria from the Global initiative for chronic Obstructive Lung Disease [GOLD]), whereas those in the Spanish cohort study were enrolled after they had had their first hospital admission due to an exacerbation of moderate-to-severe COPD.11
In the Swiss cohort we included
Results
232 patients were included in the Swiss cohort and 342 in the Spanish cohort. The Swiss cohort included elderly COPD patients with moderate-to-severe chronic airflow obstruction, a moderate degree of dyspnoea, a mean 6-min walk distance of 363 m, and a mean partial pressure of oxygen in arterial blood (PaO2) of 62·7 mm Hg (table 1). Cardiovascular comorbidity was common, and most patients received one or several inhaled drugs (table 1). Median follow-up was 34 months (range 3–50) and 3-year
Discussion
Our study showed that the original BODE index did not accurately predict mortality in two different COPD populations from Switzerland and Spain. The updated BODE index and the ADO index were similarly accurate in their risk prediction in an external validation cohort, and better than was the original BODE index. The simplified point systems for the updated BODE and ADO indices developed for patients with longstanding severe disease and patients after their first hospital admission due to an
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These authors contributed equally