COPD 'diagnosis' based on spirometric reference equations

Chronic obstructive pulmonary disease (COPD) is suspected if the ratio between forced expired volume in 1 s (FEV(1)) and forced vital capacity is below 0.7 after bronchodilatation, according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD). As this ratio varies with age and gender, the lower limit of normality (LLN) of appropriate reference equations appears more adequate.

To study the prevalences of suspected COPD according to the GOLD criterion and various reference equations in a well-defined population sample.

Spirometries obtained in a random population sample of 598 men, 50 or 60 years of age, were analysed. The prevalences of suspected COPD were calculated according to the GOLD criterion and the LLNs of four Nordic and two European reference equations.

The GOLD criterion resulted in prevalences of COPD of 9.3% and 23.7% in the 50- and 60-year-old never-smokers, respectively. Depending on the reference equation, the calculated prevalences of COPD varied between 9.3% and 23.4% and 12.0% and 39.1% among all of the 50- and 60-year-old men, respectively.

The GOLD criterion is inadequate because of substantial overestimation in 60-year-old never-smokers. LLNs of the various reference equations are unreliable because of obvious lack of consistency. Spirometric criteria for airway obstruction, and suspicion of COPD, therefore need to be revised.