Instability in the COPD Diagnosis upon Repeat Testing Vary with the Definition of COPD

BACKGROUND: A low FEV(1)/FVC from post-bronchodilator spirometry is required to diagnose COPD. Both the FEV(1) and the FVC can vary over time; therefore, individuals can be given a diagnosis of mild COPD at one visit, but have normal spirometry during the next appointment, even without an intervention. METHODS: We analyzed two population-based surveys of adults with spirometry carried out for the same individuals 5-9 years after their baseline examination. We determined the factors associated with a change in the spirometry interpretation from one exam to the next utilizing different criteria commonly used to diagnose COPD. RESULTS: The rate of an inconsistent diagnosis of mild COPD was 11.7% using FEV(1)/FVC <0.70, 5.9% using FEV(1)/FEV(6) <the lower limit of the normal range, LLN and 4.1% using the GOLD stage 2-4 criterion. The most important factor associated with diagnostic inconsistency was the closeness of the ratio to the LLN during the first examination. Inconsistency decreased with a lower FEV(1). CONCLUSIONS: Using FEV(1)/FEV(6) <LLN or GOLD stage 2-4 as the criterion for airflow obstruction reduces inconsistencies in the diagnosis of mild COPD. Further improvement could be obtained by defining a borderline zone around the LLN (e.g. plus or minus 0.6 SD), or repeating the test in patients with borderline results.