When is spirometry recommended for asthma?

Spirometry measures how much air you breathe out and how quickly you can do so. Results may be recorded before and after a reliever inhaler to see whether airflow changes. Asthma symptoms can vary from day to day, so a single test may not settle the diagnosis. Your clinician may consider your wheeze, cough, chest tightness, triggers, examination, and other breathing tests alongside spirometry.

The test is also useful when symptoms change or treatment needs review, but results must be interpreted in context rather than read as a diagnosis by themselves.

Follow the clinic's instructions about inhalers, smoking, meals, and exercise before testing; do not stop a prescribed inhaler unless the testing team tells you to. Wear loose clothing and tell staff about chest pain, recent surgery, infection, or dizziness. During the test, you will seal your lips around a mouthpiece, breathe in fully, then blow out hard and for as long as asked.

Do not wait for routine spirometry if you have severe breathlessness, cannot speak in full sentences, blue or grey lips, confusion, fainting, or little improvement after your prescribed reliever. Seek urgent care for rapidly worsening wheeze or chest tightness.

Ask whether you should use your inhaler before the appointment, what the result means for your diagnosis, and whether repeat or alternative testing is needed if your symptoms vary.