title: Estimating FVC from FEV2 and FEV3: assessment of a surrogate spirometric parameter.
abstract: BACKGROUND
  In the context that accurate measurement of FVC is important in diagnosing airflow obstruction and in assessing restriction, strategies to achieve reliable and accurate FVC measurement have drawn much attention.
  
  
  OBJECTIVE
  Because the rate of achieving end-of-test criteria during spirometry has been shown to be low, with resultant under-recording of the FVC, the current study proposes a regression equation for estimating FVC from measured values of the forced expiratory volume in 2 s (FEV2) and forced expiratory volume in 3 s (FEV3).
  
  
  METHODS
  The predictive equation for the estimated FVC from volume measurements within the first 3 s of exhalation (estimated FVC3) was generated based on 330 consecutive acceptable spirograms performed in the Cleveland Clinic Foundation Pulmonary Function Laboratory. The equation was applied to an independent validation set comprised of spirometry measurements on 370 different consecutive patients.
  
  
  RESULTS
  In the validation spirometry sample, in which the prevalence of obstruction was 34% (based on values of the measured FEV1/FVC compared to National Health and Nutrition Examination Survey III values), the sensitivity, specificity, and positive and negative predictive values of FEV1/estimated FVC3 for obstruction were 93.8%, 89.1%, 81.2%, and 96.9%, respectively. The misclassification rate was 9.2%. In the same cohort, the mean difference (+/- SD) between estimated FVC3 and measured FVC was 24.7 +/- 237 mL.
  
  
  CONCLUSIONS
  Given that FVC is frequently under-recorded, with resultant overestimation of FEV1/FVC and underdiagnosis of airflow obstruction, we believe that estimating FVC from FEV2 and FEV3 can offer practical diagnostic advantages.
authors.affiliation: Department of Pulmonary, Allergy, and Critical Care Medicine, The Cleveland Clinic Foundation, 9500 Euclid Ave A90, Cleveland, OH 44195, USA. oioac@yahoo.com
authors.forename: Octavian C
authors.initials: OC
authors.lastname: Ioachimescu
authors.forename: Saiprakash B
authors.initials: SB
authors.lastname: Venkateshiah
authors.forename: Mani S
authors.initials: MS
authors.lastname: Kavuru
authors.forename: Kevin
authors.initials: K
authors.lastname: McCarthy
authors.forename: James K
authors.initials: JK
authors.lastname: Stoller
mesh_terms: D000368:Aged; D000402:Airway Obstruction / Q000175:diagnosis* / Q000209:etiology; D015331:Cohort Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008171:Lung Diseases / Q000150:complications / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011237:Predictive Value of Tests; D013147:Spirometry; D014797:Vital Capacity