Diagnostic accuracy of pre-bronchodilator FEV(1)/FEV(6) from microspirometry to detect airflow obstruction in primary care: a randomised cross-sectional study

BACKGROUND: Forced expiratory volume in 1s/forced expiratory volume in 6 s ( FEV(1)/FEV(6)) assessment with a microspirometer may be useful in the diagnostic work up of subjects who are suspected of having COPD in primary care. AIM: To determine the diagnostic accuracy of a negative pre-bronchodilator (BD) microspirometry test relative to a full diagnostic spirometry test in subjects in whom general practitioners (GPs) suspect airflow obstruction. METHODS: Cross-sectional study in which the order of microspirometry and diagnostic spirometry tests was randomised. Study subjects were (ex-)smokers aged ⩾50 years referred for diagnostic spirometry to a primary care diagnostic centre by their GPs. A pre-BD FEV(1)/FEV(6) value <0.73 as measured with the PiKo-6 microspirometer was compared with a post-BD FEV(1)/FVC (forced vital capacity) <0.70 and FEV(1)/FVC<lower limit of normal (LLN) from diagnostic spirometry. RESULTS: One hundred and four subjects were analysed (59.6% males, 42.3% current smokers). Negative predictive values from microspirometry for airflow obstruction based on the fixed and LLN cut-off points were 94.4% (95% confidence interval (CI), 86.4–98.5) and 96.3% (95% CI, 88.2–99.3), respectively. In all, 18% of positive microspirometry results were not confirmed by a post-BD FEV(1)/FVC <0.70 and 44% of tests were false positive compared with the LLN criterion for airflow obstruction. CONCLUSIONS: Pre-bronchodilator microspirometry seems to be able to reliably preselect patients for further assessment of airflow obstruction by means of regular diagnostic spirometry. However, use of microspirometry alone would result in overestimation of airflow obstruction and should not replace regular spirometry when diagnosing COPD in primary care.