To the Editors:
“The devil's in the details” of the new American Thoracic Society (ATS)/European Respiratory Society (ERS) document regarding the interpretation of pulmonary function test (PFT) results 1. As a member of the Task Force, I was happy for the opportunity to help standardise the way in which clinically important PFTs are performed and interpreted. Unfortunately, the group spent almost all of the 3 yrs reaching an agreement (or compromise) on the mechanics of making accurate spirometry, diffusing capacity of the lung for carbon monoxide and lung volume measurements, but left inadequate time to thoroughly discuss the more important but controversial aspects of interpretation. A consensus was not reached, and thus, should not be inferred by publication of the document. In my opinion, the strategy for interpreting the presence of “obstructive abnormalities” is the detail with the highest potential for causing harm to patients.
This new strategy suggests interpreting a low forced expiratory volume in one second (FEV1)/vital capacity (VC) with a normal FEV1 as mild obstruction (see fig. 2 and table 6 in 1). Previous documents have considered this pattern as a “normal physiological variant,” normal, or borderline abnormal 2, since no associations with clinical disease or increased risk of future disease have been established for this pattern. In 2001, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines 3 were the first to consider this pattern (post-bronchodilator) to indicate mild COPD (even in patients without respiratory symptoms), followed by the ATS/ERS guidelines 4, but neither provides any evidence for this change. The latest British Thoracic Society guidelines for mild COPD 5, however, used the traditional definition of a low FEV1/forced vital capacity (FVC) and an FEV1 <80% of predicted. The apparent COPD prevalence rate is doubled when this new definition is applied to adults; and even tripled in those aged >65 yrs 6.
The new strategy also suggests interpreting the common “nonspecific” pattern of normal FEV1/VC with a low FVC (sometimes called spirometric restriction) as mild obstruction (fig. 2 in 1), at least when the total lung capacity is normal (ruling out true restriction of lung volumes). However, I'm unaware of any studies describing the clinical correlates or subsequent outcomes of groups of patients with this pattern.
If widely followed, I believe that this new strategy will: 1) more than double the apparent prevalence of mild airway obstruction; 2) increase the rate of falsely positive interpretations; 3) raise the number of prescriptions for inhaled medications for those who won't benefit from them; and 4) increase the financial, physical and psychological side-effects of these medications. A recent study from 50 sites in Europe 7 found that 75% of study participants with mild COPD (GOLD stage II) were already taking inhaled corticosteroids, despite the fact that no inhaled medication has been found to improve clinical outcomes in patients with an FEV1 >50% pred 8.
Like others before it, this new interpretative strategy is likely to be programmed into the spirometers purchased by both pulmonologists and primary care providers. When the computerised interpretation says “mild obstruction,” most doctors believe it.
- © ERS Journals Ltd
