Guide — Pulmonary Function Testing
Bronchoprovocation & Bronchodilator Response
Proving airway reactivity when spirometry is normal — the bronchodilator reversibility criteria (12% and 200 mL), the methacholine challenge and its PC20, the role of exercise challenge, and how these tests confirm or exclude asthma.
9 min read · Pulmonary Function Testing
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
When the diagnosis of asthma is uncertain, two kinds of test probe airway reactivity: bronchodilator reversibility (does obstruction improve with a bronchodilator?) and bronchoprovocation (does a challenge provoke obstruction?). Together they help confirm or argue against reactive airways.
| Test | Type | Positive Result | What It Shows |
|---|---|---|---|
| Bronchodilator reversibility | Reversibility | ≥ 12% AND ≥ 200 mL rise in FEV₁ or FVC (2005); > 10% predicted (2022) | Confirms reversible obstruction (asthma) |
| Methacholine challenge | Direct provocation | ≥ 20% fall in FEV₁ — reported as PC20 | Airway hyperresponsiveness; strong negative predictive value |
| Exercise challenge | Indirect provocation | ≈ 10–15% fall in FEV₁ after exercise | Exercise-induced bronchoconstriction |
Key Concepts
- Bronchodilator reversibility. Spirometry before and about 10–15 minutes after an inhaled short-acting bronchodilator (for example albuterol). A significant response by the classic ATS/ERS 2005 criterion is an increase of at least 12% AND at least 200 mL in FEV₁ or FVC. (The 2022 ATS/ERS update instead uses a change greater than 10% of the predicted value.) A significant response supports reversible obstruction (asthma); a negative test does not exclude it.
- Methacholine challenge.A direct bronchoprovocation: the patient inhales increasing doses of methacholine; a fall in FEV₁ of at least 20% defines a positive test, reported as the PC20 (the provocative concentration causing a 20% drop). A low PC20 means hyperresponsive airways. The test has a strong NEGATIVE predictive value — a negative methacholine challenge makes asthma unlikely.
- Exercise challenge. Exercise (or eucapnic hyperventilation, or mannitol) challenge is used for exercise-induced bronchoconstriction; a fall in FEV₁ of about 10–15% after exercise is positive.
- Pre-test withholding. Bronchodilators are held for protocol-specified intervals before reversibility and challenge testing.
Assessment & Findings
- A significant reversibility on the bronchodilator test points to reversible obstruction (asthma).
- A positive methacholine test (a low PC20) means airway hyperresponsiveness; a negative test largely rules asthma out.
- Watch the patient: bronchoprovocation can trigger significant bronchospasm, so have a bronchodilator and monitoring ready.
RT Priorities & Interventions
- Run reversibility cleanly. Get a valid baseline and the correct post-bronchodilator timing.
- Escalate methacholine safely. Step up doses, measure FEV₁ at each step, stop at a fall of 20% or more, and reverse with a bronchodilator.
- Know the limits.Recognize that a negative bronchodilator test does not rule out asthma — reactivity varies day to day.
Common Pitfalls
- Calling a sub-threshold change “reversible” — it must meet BOTH the 12% and the 200 mL criteria.
- Performing a challenge without a rescue bronchodilator and monitoring available.
- Forgetting that bronchodilators must be withheld beforehand or the test is invalid.
Board Exam Pearls
- A significant bronchodilator response is at least 12% AND at least 200 mL improvement in FEV₁ or FVC (2005); the 2022 update uses greater than 10% predicted.
- A positive methacholine challenge is a fall in FEV₁ of at least 20% (reported as the PC20); it has a strong NEGATIVE predictive value for asthma.
- A positive exercise challenge is a fall in FEV₁ of about 10–15%.
- A negative reversibility test does not exclude asthma.
- Have a rescue bronchodilator ready for any provocation test.
FAQ
What counts as a significant bronchodilator response?
By the classic ATS/ERS 2005 criterion, an increase in FEV₁ or FVC of at least 12% AND at least 200 mL from baseline after an inhaled bronchodilator. It must meet both parts. The 2022 update instead uses a change greater than 10% of the predicted value.
What is a methacholine challenge?
A direct bronchoprovocation test: the patient inhales rising doses of methacholine while FEV₁ is measured. A 20% fall in FEV₁ is positive, reported as the PC20 (the concentration that caused the drop). It is most useful for its strong negative predictive value - a negative test makes asthma unlikely.
When would I use a challenge test instead of reversibility?
When spirometry is normal or non-reversible but asthma is still suspected - the airways may be reactive only when provoked. Methacholine probes general hyperresponsiveness; an exercise or eucapnic-hyperventilation challenge targets exercise-induced bronchoconstriction.
Is bronchoprovocation safe?
It deliberately provokes bronchospasm, so it is done with continuous monitoring, spirometry at each step, clear stopping criteria (a 20% FEV₁ fall), and a rescue bronchodilator on hand to reverse the response.
Put it to work
Calculate whether a bronchodilator response is significant — the pre and post FEV₁ against the 12% and 200 mL criterion.
Open the Bronchodilator Response calculator →Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Bronchoprovocation and reversibility testing chapters.
- Coates AL, Wanger J, Cockcroft DW, et al. ERS technical standard on bronchial challenge testing: general considerations and performance of methacholine challenge tests. Eur Respir J. 2017;49(5):1601526.