What testing is recommended for diagnosing exercise-induced asthma?

Diagnostic Testing for Exercise-Induced Asthma

Indirect challenge tests are strongly recommended as the primary diagnostic method for exercise-induced asthma (EIA), with exercise challenge testing being the preferred first-line approach for patients with exercise-related symptoms. 1, 2

Exercise Challenge Testing

Protocol

• Exercise challenge test on treadmill or bicycle:
  • Duration: 6-8 minutes of high-intensity exercise
  • Intensity: Heart rate should reach and be sustained at:
    • ≥85% of maximum heart rate in adults
    • ≥95% of maximum heart rate in children and elite athletes 1, 2
  • Environmental conditions: Room temperature 20-22°C, relative humidity <40% 1, 2
  • Ventilation should reach at least 60% of maximum voluntary ventilation 1

Interpretation

• A fall in FEV₁ of ≥10% from baseline within 30 minutes post-exercise is diagnostic of EIA 1, 2
• Measurements should begin as soon as 3 minutes after exercise completion 1
• FEV₁ should be measured at multiple time points (typically 3,5,10,15, and 30 minutes post-exercise)

Alternative Indirect Challenge Tests

Eucapnic Voluntary Hyperpnea (EVH)

• Preferred for elite athletes without current asthma history 1, 2
• Protocol: Patient inhales a eucapnic gas mixture (5% CO₂, 21% O₂, balance N₂) for approximately 6 minutes 1
• Interpretation: ≥10% fall in FEV₁ is considered positive

Mannitol Challenge

• Useful as an indirect graded challenge when available 1, 2
• Increasing doses of mannitol are inhaled via dry-powder inhaler 1
• Positive test: ≥15% fall in FEV₁ from baseline or ≥10% decrease between two consecutive doses 1, 3
• High specificity (92%) and sensitivity (96%) compared to EVH 3
• Note: May be unpleasant for children and has limited availability in some countries 1

Testing Algorithm

1. Initial assessment:

   • Baseline spirometry to assess for underlying asthma 4
   • If normal baseline spirometry, proceed with challenge testing

2. Challenge test selection:

   • For patients with exercise-related symptoms: Exercise challenge test (first choice)
   • For elite competitive athletes: EVH (preferred) 1
   • When exercise or EVH testing is not feasible: Mannitol challenge (if available) 1, 2

3. If initial test is negative but EIA still suspected:

   • Consider an ungraded challenge test 1
   • Evaluate for alternative diagnoses

Differential Diagnosis Considerations

When exercise-induced symptoms persist despite negative testing or treatment, consider:

• Exercise-induced laryngeal dysfunction (EILD)
  • Diagnosis: Flexible laryngoscopy during exercise 1
• Exercise-induced hyperventilation
  • Diagnosis: Cardiopulmonary exercise testing 1
• Cardiac conditions
  • Referral to cardiologist for appropriate testing 1
• Exercise-induced anaphylaxis
  • Distinguished by systemic symptoms (pruritus, urticaria, hypotension) 1

Important Clinical Considerations

• Self-reported symptoms alone are insufficient for diagnosis 4, 5
• Direct challenges (e.g., methacholine) are less specific but more sensitive than indirect challenges 1, 2
• Running provokes EIA more easily than cycling, especially in children 1
• Empiric treatment with bronchodilators without confirmatory testing is not recommended 4
• Regular follow-up is essential as medication effectiveness may change over time due to:
  • Variability of asthma
  • Environmental conditions
  • Exercise intensity
  • Potential development of tachyphylaxis 1

By following this systematic approach to testing, exercise-induced asthma can be accurately diagnosed, allowing for appropriate treatment and improved quality of life for affected individuals.