Spirometry is objective and quantifiable, and can detect airflow limitation well before symptoms appear. Although patients with confirmed COPD have a low FEV 1 compared with age-adjusted normal values, this measurement alone may not be predictive of COPD . A more accurate indicator is the ratio of FEV1 to forced vital capacity (FVC). An FEV 1 to FVC ratio of less than 70% is generally acknowledged to indicate the presence of airflow limitation, even in the absence of physical evidence or symptoms. It is of interest that all participants in the Lung Health Study had an FEV1 to FVC ratio less than 70%, while the mean FEV 1 at study entry in these same individuals (75% predicted) was only slightly below the lower limit of normal, and a large proportion of the subjects had an FEV1 that was statistically within normal limits.