title: The relationship between FEV1 and PEF in the assessment of the severity of airways obstruction.
abstract: OBJECTIVE
  International consensus guidelines suggest that in asthma and chronic obstructive pulmonary disease (COPD), measurements of FEV1 and PEF are equivalent in the assessment of the degree of airflow obstruction when expressed as the per cent of predicted values.
  
  
  METHODS
  In this retrospective study, 2,587 paired measurements of PEF and FEV1 performed by 101 adult patients with asthma (n = 56) and COPD (n = 45) attending an outpatient chest clinic were obtained. The mean differences between FEV1 and PEF measurements when expressed as the percentage of predicted values was determined. The level of agreement between the two measurements in the classification of asthma severity (life-threatening, severe, moderate and mild asthma determined by PEF or FEV1 measurements of <30%, 30-60%, 60-80%, and >80% of the predicted values, respectively) was determined.
  
  
  RESULTS
  There was considerable variability between measurements of FEV1 and PEF when expressed as % predicted values. In both asthma and COPD, the FEV1% predicted was smaller than the PEF % predicted, with the mean difference being -10.9% (95% CI, -12.8% to -8.9%) with limits of agreement of -35.4% to +13.6%. The weighted Kappa statistic for agreement was 0.59 (95% CI, 48-70%) in the classification of the severity of airflow obstruction.
  
  
  CONCLUSIONS
  When expressed as percentage of predicted values, PEF and FEV1 values are not equivalent. We recommend that guidelines be modified to state that across the spectrum of the severity of airflow obstruction there is considerable variability between measurements of FEV1 and PEF when expressed as % predicted such that the FEV1 may be as much as 35% lower or up to 15% higher than the PEF for patients with obstructive lung diseases.
authors.affiliation: Department of Medicine, Wellington School of Medicine and Medical Research Institute of New Zealand, Wellington, New Zealand.
authors.forename: Peter
authors.initials: P
authors.lastname: Llewellin
authors.forename: Gillian
authors.initials: G
authors.lastname: Sawyer
authors.forename: Simon
authors.initials: S
authors.lastname: Lewis
authors.forename: Soo
authors.initials: S
authors.lastname: Cheng
authors.forename: Mark
authors.initials: M
authors.lastname: Weatherall
authors.forename: Penny
authors.initials: P
authors.lastname: Fitzharris
authors.forename: Richard
authors.initials: R
authors.lastname: Beasley
mesh_terms: D000328:Adult; D001249:Asthma / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D010366:Peak Expiratory Flow Rate; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012720:Severity of Illness Index