The SAFE (SGRQ score, air-flow limitation and exercise tolerance) Index: a new composite score for the stratification of severity in chronic obstructive pulmonary disease

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Abstract
Background: This study was proposed to develop a composite of outcome measures using forced expiratory volume percentage of predicted, exercise capacity and quality of life scores for assessment of chronic obstructive pulmonary disease (COPD) severity. Materials and methods: Eighty-six patients with COPD were enrolled into a prospective, observational study at the respiratory outpatient clinic, National University Hospital Malaysia (Hospital Universiti Kebangsaan Malaysia - HUKM), Kuala Lumpur. Results: Our study found modest correlation between the forced expiratory volume in 1 s (FEV1), 6 min walk distance and the SGRQ scores with mean (SD) values of 0.97 (0.56) litres/s, 322 (87) m and 43.7 (23.6)%, respectively. K-Means cluster analysis identified four distinct clusters which reached statistical significance which was refined to develop a new cumulative staging system. The SAFE Index score correlated with the number of exacerbations in 2 years (r = 0.497, pConclusion: We have developed the SGRQ, Air-Flow limitation and Exercise tolerance Index (SAFE Index) for the stratification of severity in COPD. This index incorporates the SGRQ score, the FEV1 % predicted and the 6 min walk distance. The SAFE Index is moderately correlated with the number of disease exacerbations.