Spirometric thresholds for diagnosing COPD: 0.70 or LLN, pre- or post-dilator values?

In absence of a gold standard for chronic obstructive pulmonary disease (COPD) it remains difficult to compare the true diagnostic characteristics of the forced expiratory volume in 1 second to the forced vital capacity (FEV(1)/FVC) <0.70 and < lower limit of normal (LLN). COPD is a clinical diagnosis, based on symptoms signs and lung function results combined, and an expert panel assessment would be an adequate reference standard. We compared the diagnostic properties of FEV(1)/FVC <LLN and <0.70 against this panel diagnosis: 342 participants, aged >50, consulting for persistent cough, but without physician-diagnosed COPD, were prospectively enrolled. All underwent extensive history taking, physical examination, spirometry and diffusion testing. An expert panel, including a board certified respiratory physician, assessed all diagnostic information to determine the presence or absence of COPD and served as reference standard. Then, 104 participants were diagnosed with COPD by the panel. The reproducibility of the panel diagnosis was high (kappa of 0.94). Sensitivity estimates of <0.70 were significantly higher than that of <LLN (0.73 and 0.47, respectively, p < 0.001). The fixed approach was less specific than the LLN (0.95 and 0.99, respectively, p < 0.001). There was no significant difference in diagnostic property when using pre- or post-bronchodilator FEV(1)/FVC (p = 0.615). In a symptomatic primary care population, the FEV(1)/FVC <0.70 was more accurate to detect COPD.