Inhalation Challenge Test

Aka: Inhalation Challenge Test, Inhalation Bronchial Challenge Test, Methacholine Challenge, Pulmonary Methacholine Challenge Test, Pulmonary Function Challenge Test, Bronchoprovocation

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II. Indication

  1. Suspected allergen or Exercise-Induced Asthma (despite normal lung function tests)

III. Contraindications

  1. FEV1 <65% of predicted

IV. Physiology

  1. Tests airway reactivity to airway constrictors

V. Technique

  1. Equipment to treat Status Asthmaticus readily available
  2. Pulmonary Function Tests performed at baseline
  3. Exposure to airway constrictor or irritant
    1. Methacholine (most common)
    2. Mannitol (lower Test Sensitivity than Methacholine but higher Specificity)
    3. Histamine
    4. Cold Air
    5. Hypertonic mist or hypotonic mist
  4. Pulmonary Function Tests repeated after exposure

VI. Interpretation

  1. Negative test
    1. Suggests Asthma not present
  2. Positive test criteria
    1. Methacholine
      1. Exposure to Inhaled Methacholine at 4 mg/ml or less
      2. FEV1 declines 20%
    2. Mannitol
      1. Exposure to cummulative dose of 635 mg or less of Mannitol
      2. FEV1 decline of 15% or FEV1 declines 10% between 2 consecutive doses
  3. Positive test
    1. False Positive in 8% of normal patients
    2. Asthma
    3. Emphysema
    4. Bronchiectasis
    5. Cystic Fibrosis

VII. Efficacy

  1. Methacholine Challenge
    1. Test Sensitivity: 69%
    2. Test Specificity: 80%
  2. Mannitol Inhalation
    1. Test Sensitivity: 40 to 59%
    2. Test Specificity: 78 to 100%
  3. Eucapnic Voluntary Hyperpnea
    1. Test Sensitivity: 25 to 90%
    2. Test Specificity: <71%

VIII. References

  1. Langan (2020) Am Fam Physician 101(6): 362-8 [PubMed]
  2. Crapo (2000) Am J Respir Crit Care Med 161:309-29 [PubMed]
  3. Randolph (2011) Curr Allergy Asthma 11(6): 482-90 [PubMed]

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