FEV3, FEV6 and their derivatives for detecting airflow obstruction in adult Chinese

BACKGROUND: Forced expiratory volume in 3 seconds (FEV3) and 6 seconds (FEV6) could complement FEV1 and forced vital capacity (FVC) for detecting airflow obstruction.OBJECTIVE: To compare FEV1/ FEV6 and FEV3/FVC with FEV1/FVC in the detection of airflow obstruction. METHOD: Previous lung function data were re-analysed to establish reference values for FEV3 and FEV6. Data from a separate cohort of male smokers were used as test set. FEV1, FEV3, FEV6, FVC, FEV1/FVC, FEV1/ FEV6 and FEV3/FVC were regressed against age, standing height, weight and body mass index, and the mean and 95% confidence intervals for the lower limit of normal (LLN) values for these parameters were determined.RESULTS: The percentage of smokers with airflow obstruction in the test population using FEV1/FVC < LLN was 15.0%, while using FEV1/ FEV6 < LLN and FEV3/FVC < LLN they were respectively 18.5% and 18.1%. Using FEV1/FVC < LLN as reference, the sensitivity and specificity of FEV1/ FEV6 < LLN in identifying airflow obstruction were 82.3% and 92.8%, while those for FEV3/FVC < LLN were 78.5% and 92.6%; the positive and negative predictive values were 67% and 96.7% for FEV1/ FEV6 < LLN and 65.3% and 96% for FEV3/FVC < LLN.CONCLUSION: FEV3/FVC < LLN and FEV1/ FEV6 < LLN are comparable to FEV1/FVC < LLN for detecting airflow obstruction. FEV3/FVC < LLN could be useful in screening for airflow obstruction, while FEV1/ FEV6 < LLN is useful in detecting airflow limitation in the elderly or in subjects with severe airflow obstruction.