title: Impact of switching to new spirometric reference equations on severity staging of airflow obstruction in COPD: a crosssectional observational study in primary care.
abstract: BACKGROUND
  Severity of airflow obstruction in chronic obstructive pulmonary disease (COPD) is based on forced expiratory volume in one second expressed as percentage predicted (FEV1%predicted) derived from reference equations for spirometry results.
  
  
  OBJECTIVE
  To establish how switching to new spirometric reference equations would affect severity staging of airflow obstruction in the Dutch primary care COPD patient population.
  
  
  METHODS
  Spirometry tests of 3,370 adults aged >40 years with obstruction (postbronchodilator FEV1/forced vital capacity (FVC) <0.70) were analysed. The presence and severity of obstruction were defined using Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria. Postbronchodilator FEV1%predicted was calculated using three reference equations: corrected European Community of Steel and Coal (ECSC) (currently recommended in Dutch primary care), Swanney et al., and Global Lung Initiative (GLI). Discordances between severity classifications based on these equations were analysed.
  
  
  RESULTS
  We studied 1,297 (38.5%) females and 2,073 males. Application of contemporary reference equations (i.e. Swanney and GLI) changed the GOLD severity stages obtained with the ECSC equations, mostly into milder stages. Severity of airflow obstruction was staged differently in 14.0% and 6.3%, respectively, when the Swanney et al. and GLI reference equations were applied.
  
  
  CONCLUSIONS
  Compared with the (corrected) ECSC equations, switching to more contemporary reference equations would result in lower FEV1 predicted values and affect interpretation of spirometry by reclassifying 6-14% of primary care COPD patients into different (mostly milder) severity stages. If and how this will affect GPs' treatment choices in individual patients with COPD requires further investigation.
authors.affiliation: Department of Primary and Community Care, Radboudumc, Nijmegen, The Netherlands • Department of Family Medicine, Medical Faculty of Ljubljana, University of Ljubljana, Slovenia.
authors.forename: Romina
authors.initials: R
authors.lastname: Sluga
authors.forename: Ivo J M
authors.initials: IJ
authors.lastname: Smeele
authors.forename: Annelies E
authors.initials: AE
authors.lastname: Lucas
authors.forename: Bart P
authors.initials: BP
authors.lastname: Thoonen
authors.forename: Joke G
authors.initials: JG
authors.lastname: Grootens-Stekelenburg
authors.forename: Yvonne F
authors.initials: YF
authors.lastname: Heijdra
authors.forename: Tjard R
authors.initials: TR
authors.lastname: Schermer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis*; D012016:Reference Values; D012720:Severity of Illness Index; D013147:Spirometry / Q000706:statistics & numerical data*