Development of a decision tree to assess the severity and prognosis of stable COPD

The aim of this study was to develop and validate a new method: a classification and regression tree (CART) based on easily accessible measures to predict mortality in patients with stable chronic obstructive pulmonary disease (COPD). This was a prospective study of two independent prospective cohorts: a derivation cohort with 611 recruited patients and a validation cohort with 348 patients, all followed for 5 yrs. CART analysis was used to predict 5-yr mortality risk using the following covariates from the derivation cohort: age, % predicted forced expiratory volume in 1 s (FEV1), dyspnoea, physical activity, general health and number of hospital admissions for COPD exacerbations in the previous 2 yrs. Age (>= 75 or <75 yrs) provided the first branch of the COPD-CART. The highest mortality risk (0.74) was seen in patients >75 yrs of age with higher levels of dyspnoea and FEV1 <50% pred. Patients with the lowest risk of 5-yr mortality (0.04) were <55 yrs of age with FEV1 >35% pred and one or no recent hospitalisations for COPD exacerbations. A simple decision tree that uses variables commonly gathered by physicians can provide a quick assessment of the severity of the disease, as measured by the risk of 5-yr mortality.