How does spirometry work?

You sit upright, place your lips around a disposable mouthpiece and wear a nose clip if advised. After a full breath in, you blow out as hard and as long as you can into a spirometer. The test is repeated so the clinician can check that the readings are consistent. You may be asked to repeat the measurement after using a prescribed inhaler; comparing readings can show how the airways respond.

The results include the volume of air expelled and the speed of airflow. A reduced or obstructed pattern can help a clinician investigate asthma, COPD, bronchiectasis or a chronic cough, but spirometry is interpreted alongside symptoms, examination and medical history. The test does not by itself explain every cause of breathlessness.

Wear comfortable clothing and follow the clinic’s instructions about smoking, meals and inhalers. Bring a list of medicines and explain if you have recently had a chest infection, chest pain, surgery or severe breathing trouble. During each blow, keep a firm seal around the mouthpiece and continue until the clinician tells you to stop.

Contact a clinician promptly for new or worsening breathlessness, chest pain, fainting, coughing blood or a marked change in your ability to walk or speak. Seek emergency help for severe breathing difficulty, blue lips, confusion or collapse. Do not wait for a routine lung function test when symptoms are sudden or intense.

Ask what the measurements suggest, whether you should use an inhaler before testing, and whether a repeat test is needed. You can ask how the findings fit with asthma, COPD or another explanation, and what symptoms should prompt earlier review.