Are these values in line with Global Initiative for Asthma (GINA) guidelines for diagnosing and managing asthma?

Diagnostic Values for Asthma According to GINA Guidelines

The diagnostic values mentioned align with Global Initiative for Asthma (GINA) guidelines, which recommend using multiple objective tests to confirm asthma diagnosis, with specific cut-off values for each test.

Key Diagnostic Parameters in GINA Guidelines

Spirometry and Bronchodilator Reversibility

• FEV1 or FEV1/FVC: Values less than lower limit of normal (LLN) and/or <80% predicted indicate abnormal spirometry 1, 2
• Bronchodilator Reversibility (BDR): Positive if ≥12% and/or ≥200 mL improvement after bronchodilator administration 1, 2
• Normal spirometry does not exclude asthma diagnosis when symptoms are present 1

Peak Expiratory Flow Rate (PEFR) Variability

• Significant variability defined as ≥12% in GINA and European Respiratory Society (ERS) guidelines 1, 2
• British guidelines suggest ≥20% variability with minimum change of 60 L/min, measured over at least 3 days in a week for two weeks 1
• Formula for calculation: amplitude % best = (highest – lowest) / highest × 100 1

Fractional Exhaled Nitric Oxide (FeNO)

• Cut-off value of 25 ppb recommended by ERS and GINA 1, 2
• Should ideally be performed before spirometry 1, 2
• Useful for identifying eosinophilic airway inflammation and predicting steroid responsiveness 1

Challenge Testing

• Recommended when other tests fail to confirm diagnosis 1, 2
• Options include direct bronchial challenge with methacholine or indirect testing using exercise 1, 2
• Methacholine challenge test has sensitivity of 77% and specificity of 96% with threshold PC20 of 8 mg/mL 3

Diagnostic Algorithm

1. Initial Assessment: Document presence of wheeze and other asthma symptoms (cough, breathlessness) 1

2. First-line Testing:

   • Spirometry with bronchodilator reversibility
   • FeNO measurement (ideally before spirometry)

3. If Initial Tests Inconclusive:

   • Peak flow variability monitoring over 2 weeks
   • Challenge testing (methacholine or exercise challenge)

4. Diagnosis Confirmation:

   • At least two abnormal objective test results are required for diagnosis in children 5 years and older 2
   • For adults, objective evidence of variable airflow limitation is essential

Important Considerations

• Diagnostic sensitivity of tests varies by demographic factors:

  • Methacholine challenge test has lower sensitivity in white patients (69%) compared to African American patients (95%) 3
  • Higher sensitivity in atopic (82%) versus non-atopic patients (52%) 3

• Small airway function parameters combined with FeNO can improve prediction of positive methacholine challenge test, with different optimal cut-off values based on age 4

• Uncontrolled asthma can occur at all GINA treatment steps and is associated with worse physical health outcomes and increased risk of exacerbations 5, 6

Clinical Pitfalls to Avoid

• Relying solely on symptoms without objective testing can lead to misdiagnosis
• A "trial of preventer medication" is not sufficient as a diagnostic test without objective improvement in lung function 2
• Normal spirometry between episodes does not exclude asthma; repeated testing during symptomatic periods may be necessary 1
• Challenge testing results may be affected by current controller medications, potentially reducing test sensitivity 3
• Failure to consider age, race, and atopic status when interpreting test results can affect diagnostic accuracy 3, 4

The GINA guidelines emphasize that objective lung function measurements are necessary for confirming asthma diagnosis and continued monitoring, with regular assessment recommended to evaluate treatment response and detect early deterioration 2, 7.