title: Peak expiratory flow rate as a surrogate for forced expiratory volume in 1 second in COPD severity classification in Thailand.
abstract: BACKGROUND
  There are limited studies directly comparing correlation and agreement between peak expiratory flow rate (PEFR) and forced expiratory volume in 1 second (FEV1) for severity classification of COPD. However, clarifying the role of PEFR as a surrogate of COPD severity classification instead of FEV1 is essential in situations and areas where spirometry is not routinely available.
  
  
  OBJECTIVE
  To evaluate the agreement between FEV1 and PEFR using Global initiative for chronic Obstructive Lung Disease (GOLD) severity classification criteria.
  
  
  METHODS
  This cross-sectional study included stable COPD patients. Both absolute values and % predicted FEV1 and % predicted PEFR were obtained from the same patients at a single visit. The severity of COPD was classified according to GOLD criteria. Pearson's correlation coefficient was used to examine the relationship between FEV1 and PEFR. The agreement of % predicted FEV1 and % predicted PEFR in assigning severity categories was calculated using Kappa statistic, and identification of the limits of agreement was by Bland-Altman analysis. Statistical significance was set at P-value <0.05.
  
  
  RESULTS
  Three hundred stable COPD patients were enrolled; 195 (65.0%) male, mean age 70.4±9.4 years, and mean % predicted FEV1 51.4±20.1. Both correlations between the % predicted FEV1 and PEFR as well as the absolute values were strongly significant (r=0.76, P<0.001 and r=0.87, P<0.001, respectively). However, severity categories of airflow limitation based on % predicted FEV1 or PEFR intervals were concordant in only 179 patients (59.7%). The Kappa statistic for agreement was 0.41 (95% confidence interval, 0.34-0.48), suggesting unsatisfied agreement. The calculated limits of agreement were wide (+27.1% to -28.9%).
  
  
  CONCLUSIONS
  Although the correlation between FEV1 and PEFR measurements were strongly significant, the agreement between the two tests was unsatisfied and may influence inappropriate clinical decision making in diagnosis, severity classification, and management of COPD.
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Chaicharn
authors.initials: C
authors.lastname: Pothirat
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Warawut
authors.initials: W
authors.lastname: Chaiwong
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Nittaya
authors.initials: N
authors.lastname: Phetsuk
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Chalerm
authors.initials: C
authors.lastname: Liwsrisakun
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Chaiwat
authors.initials: C
authors.lastname: Bumroongkit
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Athavudh
authors.initials: A
authors.lastname: Deesomchok
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Theerakorn
authors.initials: T
authors.lastname: Theerakittikul
authors.affiliation: Division of Pulmonary, Critical Care and Allergy, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Atikun
authors.initials: A
authors.lastname: Limsukon
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D012720:Severity of Illness Index; D013147:Spirometry; D013785:Thailand
keywords: agreement; chronic obstructive pulmonary disease; spirometry