title: Diagnostic accuracy of FEV1/forced vital capacity ratio z scores in asthmatic patients.
abstract: BACKGROUND
  The FEV1/forced vital capacity (FVC) ratio is used as a criterion for airflow obstruction; however, the test characteristics of spirometry in the diagnosis of asthma are not well established. The accuracy of a test depends on the pretest probability of disease.
  
  
  OBJECTIVE
  We wanted to estimate the FEV1/FVC ratio z score threshold with optimal accuracy for the diagnosis of asthma for different pretest probabilities.
  
  
  METHODS
  Asthmatic patients enrolled in 4 trials from the Asthma Clinical Research Centers were included in this analysis. Measured and predicted FEV1/FVC ratios were obtained, with calculation of z scores for each participant. Across a range of asthma prevalences and z score thresholds, the overall diagnostic accuracy was calculated.
  
  
  RESULTS
  One thousand six hundred eight participants were included (mean age, 39 years; 71% female; 61% white). The mean FEV1 percent predicted value was 83% (SD, 15%). In a symptomatic population with 50% pretest probability of asthma, optimal accuracy (68%) is achieved with a z score threshold of -1.0 (16th percentile), corresponding to a 6 percentage point reduction from the predicted ratio. However, in a screening population with a 5% pretest probability of asthma, the optimum z score is -2.0 (second percentile), corresponding to a 12 percentage point reduction from the predicted ratio. These findings were not altered by markers of disease control.
  
  
  CONCLUSIONS
  Reduction of the FEV1/FVC ratio can support the diagnosis of asthma; however, the ratio is neither sensitive nor specific enough for diagnostic accuracy. When interpreting spirometric results, consideration of the pretest probability is an important consideration in the diagnosis of asthma based on airflow limitation.
authors: Department of Medicine, Division of Pulmonary and Critical Care, Johns Hopkins University, Baltimore, Md. Electronic address: alamber5@jhmi.edu.
authors: Allison
authors: A
authors: Lambert
authors: Department of Medicine, Division of Pulmonary and Critical Care, Johns Hopkins University, Baltimore, Md.
authors: M Bradley
authors: MB
authors: Drummond
authors: Department of Medicine, Division of Pulmonary and Critical Care, Johns Hopkins University, Baltimore, Md.
authors: Christine
authors: C
authors: Wei
authors: Department of Medicine, Division of Pulmonary and Critical Care, University of Vermont, Burlington, Vt.
authors: Charles
authors: C
authors: Irvin
authors: Department of Medicine, Division of Pulmonary and Critical Care, University of Vermont, Burlington, Vt.
authors: David
authors: D
authors: Kaminsky
authors: Department of Medicine, Division of Pulmonary and Critical Care, Johns Hopkins University, Baltimore, Md.
authors: Meredith
authors: M
authors: McCormack
authors: Department of Medicine, Division of Pulmonary and Critical Care, Johns Hopkins University, Baltimore, Md.
authors: Robert
authors: R
authors: Wise
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000175:diagnosis* / Q000208:ethnology / Q000503:physiopathology; D001249:Asthma / Q000175:diagnosis* / Q000208:ethnology / Q000503:physiopathology; D015415:Biomarkers / Q000032:analysis; D044383:Black People; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011336:Probability; D013147:Spirometry; D014797:Vital Capacity; D044465:White People
chemical_list: D015415:Biomarkers
keywords: Asthma; accuracy; airflow obstruction; spirometry; z score