What is spirometry? Spirometry is a standard test doctors use to measure how well your lungs are functioning. The test works by measuring airflow into and out of your lungs. To take a spirometry test, you sit and breathe into a small machine called a spirometer. This medical device records the amount of air you breathe in and out and the speed of your breath. Spirometry tests are used to diagnose these conditions: COPD asthma restrictive lung disease (such as interstitial pulmonary fibrosis) other disorders affecting lung function