FEV(1)/FEV(6) to diagnose airflow obstruction. Comparisons with computed tomography and morbidity indices.
BACKGROUND
FVC is a difficult maneuver for many patients, and forced expiratory volume in 6 seconds (FEV6) has been proposed as a surrogate for FVC for the diagnosis of chronic obstructive pulmonary disease (COPD). Previous studies have performed head-to-head comparisons of these thresholds but did not examine their relationships with structural lung disease, symptoms, or exacerbations.


OBJECTIVE
To compare FEV1/FEV6 with FEV1/FVC in the diagnosis of COPD-related morbidity and structural lung disease as assessed by CT.


METHODS
We analyzed data from a large multicenter cohort study (COPDGene) that included current and former smokers (age 45-80 yr). Accuracy and concordance between the two ratios in diagnosing structural COPD was compared using CT measures of emphysema and airway disease and COPD-related morbidity to assess how the two ratios compare in defining disease.


RESULTS
A total of 10,018 subjects were included. FEV1/FEV6 showed excellent accuracy in diagnosing airflow obstruction using FEV1/FVC < 0.70 as a reference (area under curve, 0.99; 95% confidence interval [CI], 0.989-0.992; P < 0.001). FEV1/FEV6 < 0.73 had the best sum of sensitivity (92.1%; 95% CI, 90.8-92.4) and specificity (97.3%; 95% CI, 97.3-98.1). There was excellent agreement between the two diagnostic cutoffs (κ = 0.90; 95% CI, 0.80-0.91; P < 0.001). In comparison with control subjects and those positive by FEV1/FVC alone, subjects positive by FEV1/FEV6 alone had greater gas trapping and airway wall thickness, worse functional capacity, and a greater number of exacerbations on follow-up. These relationships held true when disease definitions were made using the lower limits of normal.


CONCLUSIONS
FEV1/FEV6 can be substituted for FEV1/FVC in diagnosing airflow obstruction and may better predict COPD-related pathology and morbidity.
1 UAB Lung Health Center, Division of Pulmonary, Allergy and Critical Care Medicine, and.
Surya P
SP
Bhatt
Young-Il
YI
Kim
James M
JM
Wells
William C
WC
Bailey
Joe W
JW
Ramsdell
Marilyn G
MG
Foreman
Robert L
RL
Jensen
Douglas S
DS
Stinson
Carla G
CG
Wilson
David A
DA
Lynch
Barry J
BJ
Make
Mark T
MT
Dransfield
D000368:Aged; D000369:Aged, 80 and over; D000402:Airway Obstruction / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D011788:Quality of Life; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D014797:Vital Capacity / Q000502:physiology