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.