What to know about spirometry for asthma and COPD

The test supports diagnosis and monitoring, but it is interpreted alongside symptoms, medical history, examination findings and, when needed, other tests. A result on its own does not establish which condition is present.

You breathe into a spirometer after filling your lungs, then blow out as hard and as completely as you can. Repeating the manoeuvre helps the clinician check that the readings are consistent and technically usable.

Asthma can cause variable airflow narrowing, so a clinician may repeat spirometry after a reliever medicine or compare readings taken at different times. COPD more often produces airflow limitation that remains after a bronchodilator. These patterns guide assessment, but symptoms and exposure history still matter because results can overlap or be affected by effort, a recent respiratory infection, or another lung condition.

Follow the clinic's instructions about inhalers because some medicines may need to be withheld before testing, while others should be continued. Do not stop prescribed treatment unless the testing team has specifically told you when and how to do so.

Wear loose clothing, avoid a heavy meal immediately beforehand, and tell the clinician about a recent chest infection, surgery, heart problem, dizziness with forceful breathing, or pregnancy. Bring your inhalers and a current medicine list. During the test, seal your lips around the mouthpiece and follow the coach's prompts; tell them promptly if you feel faint, develop chest pain, or need to stop.

Spirometry is not a substitute for urgent assessment during severe breathing difficulty. Seek emergency care if you are struggling to breathe, cannot speak in full sentences, develop blue or grey lips, become confused or unusually drowsy, faint, or have severe chest pain.

If wheeze, cough, chest tightness or breathlessness is worsening but not severe, arrange a prompt clinical review. Use prescribed rescue treatment according to your personal action plan while seeking care; do not delay help in order to complete a breathing test.

Ask whether the test quality was adequate, whether airflow limitation was present, and whether it changed after a bronchodilator. It is also useful to clarify whether your symptoms fit asthma, COPD, or another cause; whether further testing is needed; and how the result affects inhaler use, smoking cessation support, follow-up, or a written action plan.