Direct bronchoprovocation test methods: history 1945-2018.

Area of Science:

• Respiratory Medicine
• Clinical Immunology
• Pulmonary Function Testing

Background:

• Bronchoprovocation inhalation challenge tests with direct-acting stimuli like methacholine are standard clinical tools for asthma diagnosis.
• The historical development of these tests, from parenteral administration to inhalation challenges monitored by FEV1, is reviewed.
• Standardization of challenge methods, particularly the methacholine provocative dose 20 (PD20), is critical for accurate interpretation.

Observation:

• The methacholine inhalation test demonstrates high sensitivity for diagnosing current asthma, especially when symptoms are current and deep inhalations are avoided.
• A methacholine PD20 exceeding 400 μg provides reasonable certainty in excluding current asthma under specific testing conditions.
• PD20 values between 25 μg and 400 μg show variable specificity and positive predictive value, influenced by the exact PD20 and pre-test asthma probability.

Findings:

• A methacholine PD20 > 400 μg is recommended for a negative asthma challenge, indicating the absence of current asthma.
• Lower PD20 values (≤ 400 μg) suggest potential asthma, with specificity and predictive value increasing as the PD20 decreases.
• A PD20 ≤ 25 μg is highly specific but has low sensitivity for asthma diagnosis.

Implications:

• Standardized methacholine challenge protocols are essential for reliable asthma diagnosis.
• Understanding the diagnostic performance of different PD20 thresholds aids in clinical decision-making.
• Accurate interpretation of methacholine challenge results, considering sensitivity and specificity, improves patient management.