For several hours prior to the spirometry test, a patient should refrain from exercise, eating a heavy meal and smoking. These can interfere with respiration during testing. A patient’s physician may also have specific instructions on the use of bronchodilators or inhaler medications prior to the test. Patients should always check with their physician before suspending the use of any medications.

Wearing loose-fitting clothes to the test is a good idea, as it allows the patient to breathe without restriction. Patients who wear dentures should keep them in for the test, as the dentures will make it easier for the patient to create a tight seal on the mouthpiece of the spirometer.

If the patient being tested is a child, parents are encouraged to review the testing procedure with them in advance so they are not overly frightened by the testing itself.

Spirometry testing is quick, painless and noninvasive. The test is usually performed on a simple spirometer machine located at a physician’s office, hospital or clinic. Though some spirometers are small enough to be portable, the devices are not capable of producing highly accurate results.

The test is usually administered by a physician or qualified technician. The test procedure is as follows:

1. Patients place the mouthpiece of the spirometer in their mouth, while standing or sitting up as straight as possible. If they are unable to create a tight seal around the mouthpiece, patients should notify the person conducting the test of the problem. This is important because a poor seal can lead to poor results that do not permit interpretation.
   
   
2. Nose clips are applied to the patient, preventing them from breathing through their nose.
   
   
3. The physician or technician may have patients go through several breathing exercises or tests, which will be explained to patients during the procedure.
   
   
4. Patients are instructed to inhale as much air into the lungs as possible, then exhale that air as fast and for as long as possible.
   
   
5. Patients remove the mouthpiece and breathe normally.

Some physicians will perform the test once under normal circumstances, and then administer a bronchodilator to the patient before repeating the test. This allows the physician to see whether the patient’s breathing can be improved with the use of bronchodilators. Some doctors will perform the test several times in a short period of time in order to achieve more accurate results.

Because the test involves heavy breathing it can make some patients temporarily short of breath. Patients should inform the person conducting the test if breathing difficulties persist or if they begin to feel dizzy. Testing will cease and treatment to resolve symptoms will immediately be given.

A physician or healthcare provider will often explain the spirometry test results to patients immediately after the test is complete. In some cases, a follow-up conversation or office visit may be scheduled to go over the results.

Although spirometry results can identify restrictive or obstructive disease patterns, the results are not disease specific. As a result, a physician may need to perform additional tests (e.g., chest x-ray) to determine whether asthma, emphysema or another disease is causing the abnormality.  

It is also important to note that while spirometry can detect obstructive diseases in their early stages, it is not always sensitive enough to detect restrictive diseases (e.g., silicosis, pneumonoconiosis) before extensive and irreversible damage has occurred.