title: Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction.
abstract: OBJECTIVE
  The prevalence of airway obstruction varies widely with the definition used.
  
  
  OBJECTIVE
  To study differences in the prevalence of airway obstruction when applying four international guidelines to three population samples using four regression equations.
  
  
  METHODS
  We collected predicted values for forced expiratory volume in 1 s/forced vital capacity (FEV(1)/FVC) and its lower limit of normal (LLN) from the literature. FEV(1)/FVC from 40 646 adults (including 13 136 asymptomatic never smokers) aged 17-90+years were available from American, English and Dutch population based surveys. The prevalence of airway obstruction was determined by the LLN for FEV(1)/FVC, and by using the Global Initiative for Chronic Obstructive Lung Disease (GOLD), American Thoracic Society/European Respiratory Society (ATS/ERS) or British Thoracic Society (BTS) guidelines, initially in the healthy subgroup and then in the entire population.
  
  
  RESULTS
  The LLN for FEV(1)/FVC varied between prediction equations (57 available for men and 55 for women), and demonstrated marked negative age dependency. Median age at which the LLN fell below 0.70 in healthy subjects was 42 and 48 years in men and women, respectively. When applying the reference equations (Health Survey for England 1995-1996, National Health and Nutrition Examination Survey (NHANES) III, European Community for Coal and Steel (ECCS)/ERS and a Dutch population study) to the selected population samples, the prevalence of airway obstruction in healthy never smokers aged over 60 years varied for each guideline: 17-45% of men and 7-26% of women for GOLD; 0-18% of men and 0-16% of women for ATS/ERS; and 0-9% of men and 0-11% of women for BTS. GOLD guidelines caused false positive rates of up to 60% when applied to entire populations.
  
  
  CONCLUSIONS
  Airway obstruction should be defined by FEV(1)/FVC and FEV(1) being below the LLN using appropriate reference equations.
authors.affiliation: Respiratory Physiology Laboratory, Christchurch Hospital, Private Bag 4710, Christchurch 8140, New Zealand. maureen.swanney@cdhb.govt.nz
authors.forename: M P
authors.initials: MP
authors.lastname: Swanney
authors.forename: G
authors.initials: G
authors.lastname: Ruppel
authors.forename: P L
authors.initials: PL
authors.lastname: Enright
authors.forename: O F
authors.initials: OF
authors.lastname: Pedersen
authors.forename: R O
authors.initials: RO
authors.lastname: Crapo
authors.forename: M R
authors.initials: MR
authors.lastname: Miller
authors.forename: R L
authors.initials: RL
authors.lastname: Jensen
authors.forename: E
authors.initials: E
authors.lastname: Falaschetti
authors.forename: J P
authors.initials: JP
authors.lastname: Schouten
authors.forename: J L
authors.initials: JL
authors.lastname: Hankinson
authors.forename: J
authors.initials: J
authors.lastname: Stocks
authors.forename: P H
authors.initials: PH
authors.lastname: Quanjer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003951:Diagnostic Errors; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic / Q000592:standards; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis*; D012016:Reference Values; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult