title: Methacholine challenge test: diagnostic characteristics in asthmatic patients receiving controller medications.
abstract: BACKGROUND
  The methacholine challenge test (MCT) is commonly used to assess airway hyperresponsiveness, but the diagnostic characteristics have not been well studied in asthmatic patients receiving controller medications after the use of high-potency inhaled corticosteroids became common.
  
  
  OBJECTIVE
  We investigated the ability of the MCT to differentiate participants with a physician's diagnosis of asthma from nonasthmatic participants.
  
  
  METHODS
  We conducted a cohort-control study in asthmatic participants (n= 126) who were receiving regular controller medications and nonasthmatic control participants (n= 93) to evaluate the sensitivity and specificity of the MCT.
  
  
  RESULTS
  The overall sensitivity was 77% and the specificity was 96% with a threshold PC(20) (the provocative concentration of methacholine that results in a 20% drop in FEV(1)) of 8 mg/mL. The sensitivity was significantly lower in white than in African American participants (69% vs 95%, P= .015) and higher in atopic compared with nonatopic (82% vs 52%, P= .005). Increasing the PC(20) threshold from 8 to 16 mg/mL did not noticeably improve the performance characteristics of the test. African American race, presence of atopy, and lower percent predicted FEV(1) were associated with a positive test result.
  
  
  CONCLUSIONS
  The utility of the MCT to rule out a diagnosis of asthma depends on racial and atopic characteristics. Clinicians should take into account the reduced sensitivity of the MCT in white and nonatopic asthmatic patients when using this test for the diagnosis of asthma.
authors.affiliation: Department of Medicine, Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St Louis, MO 63110, USA. ksumino@dom.wustl.edu
authors.forename: Kaharu
authors.initials: K
authors.lastname: Sumino
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Sugar
authors.forename: Charles G
authors.initials: CG
authors.lastname: Irvin
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
authors.forename: Dave
authors.initials: D
authors.lastname: Shade
authors.forename: Christine Y
authors.initials: CY
authors.lastname: Wei
authors.forename: Janet T
authors.initials: JT
authors.lastname: Holbrook
authors.forename: Robert A
authors.initials: RA
authors.lastname: Wise
authors.forename: Mario
authors.initials: M
authors.lastname: Castro
mesh_terms: D000293:Adolescent; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use*; D000328:Adult; D000368:Aged; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use*; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy*; D016535:Bronchial Hyperreactivity / Q000175:diagnosis / Q000188:drug therapy; D001985:Bronchial Provocation Tests / Q000379:methods*; D002648:Child; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D008875:Middle Aged; D011237:Predictive Value of Tests; D012129:Respiratory Function Tests; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000305:Adrenal Cortex Hormones; D018927:Anti-Asthmatic Agents; D016210:Methacholine Chloride