title: The relationship between FEV1 and peak expiratory flow in patients with airways obstruction is poor.
abstract: OBJECTIVE
  To evaluate the correlation between FEV1 and peak expiratory flow (PEF) values expressed as a percentage of their predicted value, and to assess factors influencing differences between the two measurements.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  Pulmonary function laboratory at a tertiary-level teaching hospital in northern India.
  
  
  METHODS
  A total of 6,167 adult patients showing obstructive pattern on spirometry over a 6-year period.
  
  
  METHODS
  None.
  
  
  RESULTS
  There was considerable variability between percentage of predicted FEV1 (FEV1%) and percentage of predicted PEF (PEF%). Locally weighted least-square modeling revealed that PEF% underestimated [corrected] FEV1% in patients with less severe obstruction and overestimated [corrected] it in those with more severe obstruction. Using Bland-Altman analysis, PEF% underestimated FEV1% by a mean of only 0.7%; however, limits of agreement were wide (- 27.4 to + 28.8%), indicating that these two measurements cannot be used interchangeably. PEF% and FEV1% were > 5% apart in approximately three fourths and differed by > 10% in approximately one half of the patients. On multivariate analysis, discordance > 5% was significantly influenced by female gender (odds ratio, 1.26; 95% confidence interval [CI], 1.01 to 1.58) and increasing FEV1% (odds ratio, 1.09 for every 10% increase; 95% CI, 1.04 to 1.14) but not by height or age.
  
  
  CONCLUSIONS
  FEV1% and PEF% are not equivalent in many patients, especially women and those with less severe airflow limitation. Assumptions of parity between PEF% and FEV1% must be avoided.
authors.affiliation: Department of Pulmonary Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh 160012, India.
authors.forename: Ashutosh N
authors.initials: AN
authors.lastname: Aggarwal
authors.forename: Dheeraj
authors.initials: D
authors.lastname: Gupta
authors.forename: Surinder K
authors.initials: SK
authors.lastname: Jindal
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000402:Airway Obstruction / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010366:Peak Expiratory Flow Rate / Q000502:physiology*; D011237:Predictive Value of Tests; D012044:Regression Analysis