How long does spirometry take to work for asthma?

The test measures how much air you breathe out and how quickly you can blow it out. For asthma, results may be compared before and after a reliever inhaler, or reviewed alongside your symptoms and peak-flow pattern. A normal result on one day does not always exclude asthma because airway narrowing can vary. The clinician may need other testing or repeat measurements before confirming the diagnosis.

Follow the clinic's instructions about inhalers, meals, smoking and strenuous activity before testing; do not stop a prescribed inhaler unless the testing team tells you to. Wear comfortable clothing and expect several strong blows with rest between attempts. Tell the clinician if you feel dizzy, cough heavily or cannot complete a manoeuvre. Ask when and how the result will be explained.

Spirometry is not a substitute for urgent asthma care. Use your asthma action plan and seek emergency help for severe breathlessness, inability to speak in full sentences, blue lips, collapse or a reliever inhaler that is not helping. Arrange prompt review when wheeze or night symptoms are becoming more frequent.

Ask whether you should withhold any inhaler, whether bronchodilator testing is planned, what your measurements show, and what happens if the result is inconclusive. Ask for a written action plan if asthma is diagnosed.