How effective is spirometry for asthma?

The test measures how much air you breathe out and how quickly you can exhale. A clinician may compare readings before and after an inhaled bronchodilator. Improvement after the medicine can support asthma when it fits the pattern of variable symptoms, such as wheeze, chest tightness, cough or breathlessness.

A normal reading does not rule out asthma, especially when symptoms come and go or are absent on the test day. A reading can also be affected by effort, technique, recent medicines and other lung conditions. Your clinician may therefore consider repeat testing, peak-flow monitoring or another breathing assessment.

Follow the appointment instructions about inhalers and avoid strenuous activity or a heavy meal shortly before testing if your clinic advises this. Wear comfortable clothing and tell the clinician about medicines, smoking, recent infections and symptoms during exercise or at night.

During the test, a tight seal around the mouthpiece and a strong, sustained exhalation help produce a reliable reading. Several attempts are normal. Use the result as one part of a plan that may include trigger control, inhaler technique review and treatment adjustment.

Arrange medical review for recurring wheeze, night-time cough, breathlessness or symptoms that limit activity, even if a previous spirometry result was normal. Seek urgent help for severe breathing difficulty, blue or grey lips, confusion, fainting, or trouble speaking in full sentences. Follow your personal asthma action plan if you have one.

Ask what your numbers indicate, whether the test was technically satisfactory, if inhalers should be paused before a repeat test, and what other explanation will be considered if symptoms continue.