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Spirometry (Pulmonary Function Testing)


Why it's done

How you prepare

What you can expect

When you go to take your test




Spirometry is a common office test used to diagnose asthma, chronic obstructive pulmonary disease (COPD) and certain other conditions that affect breathing. Spirometry may also be used periodically to check how well your lungs are working once you're being treated for a chronic lung condition.

Spirometry measures how much air you can inhale and how much you can exhale. Spirometry also measures how fast you can exhale. Spirometry values below average indicate your lungs aren't working as well as they should.

Why it's done

Spirometry is done to diagnose asthma, COPD and other lung conditions or to look for other causes of breathing trouble. Your doctor may suggest a spirometry test if he or she suspects your symptoms are caused by a chronic lung condition such as:


Chronic obstructive pulmonary disease (COPD)

Chronic bronchitis


Pulmonary fibrosis

If you've already been diagnosed with a chronic lung disorder, spirometry may be used periodically to check how well your medications are working and whether your symptoms are under control.

How you prepare

Follow your doctor's instructions about whether you should avoid use of inhaled breathing medications or other medications before the test. Other steps to take include:

Wear loose fitting clothing that won't interfere with your ability to take a deep breath.

Avoid eating a large meal before your test, which will make it easier to breathe.

What you can expect

Your spirometry test will take about five to 10 minutes for one set of measurements.

If your doctor gives you an inhaled medication to open your lungs (bronchodilator) after your initial test, you'll need to wait 15 minutes and then you'll have another set of measurements done. That way your doctor can compare the results of the two measurements, to see whether the bronchodilator improved your airflow.

When you go to take your test

The nurse or technician will give you specific instructions about how to take the test. Listen carefully and make sure you know exactly what to do. Doing the test incorrectly will cause inaccurate results.

The nurse or technician will have you take a deep breath and breathe out as hard as you can for several seconds into a tube that's attached to a machine (spirometer). You may feel short of breath for a moment after you perform the test.

You'll need to repeat the test at least three times to make sure your results are accurate.

Your doctor may give you a bronchodilator as part of the test. This can help identify the extent of your breathing obstruction, and can help your doctor determine whether you need medication to help you breathe.

Because this spirometry requires following instructions and forcefully exhaling, this test is generally not useful in children who are under 5 years old.


Key spirometry measurements include:

Forced vital capacity (FVC). This is the largest amount of air that you can forcefully exhale after breathing in as deeply as you can. A lower than normal FVC reading indicates restricted breathing.

Forced expiratory volume (FEV-1). This is how much you can force from your lungs in one second.

Your doctor will use a fraction of your FEV-1 divided by your FVC to determine a percentage that's compared with the average results of people of your same height, age and sex to determine how well your lungs are functioning. These numbers give an indication of how well your lungs are working.

Your doctor may also use other calculations from your test to calculate your lung function. The test will generate a graph known as a flow-volume loop. Looking at this graph of your breathing during the test may further help your doctor evaluate your breathing.

Even if your spirometry tests are normal, it's no guarantee you don't have asthma or another chronic lung condition. If your initial spirometry results are normal, but your doctor still suspects you have a lung condition that interferes with breathing, you may need to take additional tests. One such test is a bronchial challenge test. With this test, you'll inhale a drug such as methacholine. If your airways tighten and your lung function measurements decrease, you may have asthma.

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