Asthma breathing tests: what spirometry can show

A clinician may compare readings before and after a bronchodilator medicine. An improvement after the medicine can support an asthma assessment, but the result is interpreted alongside symptoms, examination findings and medical history.

You take the deepest breath you can, seal your lips around a mouthpiece and blow out hard and fast until instructed to stop. The spirometer records the total volume exhaled and the amount expelled early in the breath. Several attempts may be needed so the clinician can check that the effort is consistent.

Narrowed airways can reduce or slow the exhaled airflow. A normal reading does not automatically exclude asthma because airway narrowing may vary over time. If symptoms and spirometry do not align, the clinician may repeat testing when symptoms are present or consider another type of breathing assessment.

Follow the clinic's instructions about inhalers before the test; do not stop prescribed medicine unless the clinic specifically tells you to. Bring your inhalers and a list of medicines. Wear clothing that does not restrict your chest or abdomen, and mention a recent infection, surgery, chest pain, dizziness or pregnancy before testing begins.

Tell the technician if you feel faint, develop chest discomfort or cannot continue. Strong coaching is normal because the accuracy of spirometry depends on a tight mouth seal, a rapid start and sustained effort. Ask when and how you will receive the interpretation rather than relying on the displayed numbers alone.

Spirometry is not the priority during severe breathing distress. Seek emergency help if you are struggling to breathe, cannot speak in full sentences, become unusually drowsy or confused, develop blue or grey lips, or get little relief from the reliever medicine in your asthma plan. Do not delay urgent care to arrange a breathing test.

Ask whether you should use your usual inhalers on the test day, whether bronchodilator testing is planned, and whether your effort produced reliable readings. You can also ask how the result fits your symptom pattern, whether repeat testing is appropriate and what treatment changes, if any, the findings support.