Quality of life measured by the St George's Respiratory Questionnaire and spirometry

¹ University of Otago Wellington, Wellington, New Zealand
² Medical Research Institute of New Zealand, Wellington, New Zealand

^* To whom correspondence should be addressed. E-mail: Richard.Beasley{at}mrinz.ac.nz.

	Abstract

We aimed to determine if the criteria for the diagnosis of COPD and its classification by severity as recommended by the Global Initiative for Obstructive Lung Disease are supported by measurements of respiratory health-related quality of life.

A community-based sample of adults aged 25 to 75 years had pre- and post-bronchodilator spirometry and completed the St George's Respiratory Questionnaire (SGRQ). Loess scatter plot smoothers of SGRQ versus post-bronchodilator FEV₁/FVC ratio and post-bronchodilator FEV₁ as percent predicted together with receiver operating characteristic (ROC) curve analysis were used to determine the relationship between spirometric variables and clinically important differences in the SGRQ score.

The scatter plot smoother and ROC curve analyses supported the value of 0.7 for post-bronchodilator FEV₁/FVC, which was about four units higher than the nadir of the SGRQ. To represent a distance of eight units on SGRQ, the cut-points for post-bronchodilator FEV₁ that delimit COPD severity stages were 80%, 60% and 40% predicted.

To diagnose COPD the use of a post-bronchodilator FEV₁/FVC of 0.7 is supported by health-related quality of life measurements. There may be advantages in using FEV₁ cut-points of 80%, 60% and 40% predicted for the classification of mild, moderate and severe COPD, similar to the approach recommended for asthma.