Spirometers are a very useful tool for a doctor to diagnose breathing conditions such as chronic obstructive disease (COPD) and lung capacity in general for those who present symptoms of concern. They are a great diagnostic tool for those who are currently under treatment for lung conditions to see if the treatment is effective. It measures the flow of air going in and out of the lungs and how fast it is moving.

When used on patients who currently have a lung condition, it can show the efficacy of medication that was prescribed and to monitor symptoms. Conditions such as asthma, COPD, pulmonary fibrosis, chronic bronchitis, or emphysema can be diagnosed with this test.

Before taking the test, patients are advised not to use any medications or inhalants for the most accurate readings. Large meals should be avoided in order to breath easier and loose clothing is recommended so that the patient will not be constricted in their breathing.

Before the test begins a soft clip will be placed on the nose to prevent air from escaping though it as well as a mouthpiece filter will be used to guard against contaminants. A deep breath will be taken and then exhaled as hard as is possible into the mouthpiece on the spirometer to test air flow. This can cause one to feel dizzy for a bit or have shortness of breath. One may be asked to repeat this three times to get an accurate reading.

If inhaled medications are administered after the initial test to keep the lungs open, one should wait at least 15 minutes before taking another test. Comparison can then be made between the two tests to see if the medication improved airflow. Each test takes less than 15 minutes to do. The measurements include the largest amount of air that can be exhaled, called forced vital capacity (FVC), and another reading shows how much air can be exhaled in one second, known as forced expiratory volume (FEV-1).

This test is used to detect respiratory disease in patients who present symptoms of breathlessness, to diagnose and manage asthma, and to distinguish respiratory conditions from those of cardiac disease. It is used to differentiate between obstructive and restrictive lung disease, measure bronchial responsiveness, identify risk of pulmonary barotrauma in scuba divers, and assess impairment from occupational asthma. Risk assessment before anesthesia or cardiothoracic surgery can be measured as well as detection of vocal cord dysfunction and the ongoing treatment of existing lung conditions.

In order for this test to show accurate results, the patient needs to be cooperative. It can be used on children, but it is advised that they be at least 6 years of age or more. It is not a good test for those who are heavily sedated, have limited respiratory effort, are unconscious, or cannot understand the instructions.

Spirometers can check for the effects of medication usage such as histamine or a methacholine agents, check the hyper-responsiveness to either inhalation of dry or cold air, or provide bronchial challenge testing. Some other lung tests that can be performed are a plethysmography or nitrogen washout.