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Lung function tests (also called pulmonary
function tests, or PFTs) check how well your lungs work. The tests determine
how much air your
lungs can hold, how quickly you can move air in and
out of your lungs, and how well your lungs put oxygen into and remove carbon
dioxide from your blood. The tests can diagnose lung diseases, measure the
severity of lung problems, and check to see how well treatment for a lung
disease is working.
Other tests—such as residual volume, gas
diffusion tests, body plethysmography, inhalation challenge tests, and exercise
stress tests—may also be done to determine lung function.
Spirometry is the first and most commonly done lung function
test. It measures how much and how quickly you can move air out of your lungs.
For this test, you breathe into a mouthpiece attached to a recording device
(spirometer). The information collected by the spirometer may be printed out on
a chart called a spirogram.
The more common lung function values
measured with spirometry are:
Gas diffusion tests measure
the amount of
oxygen and other gases that cross the lungs' air sacs (alveoli) per minute.
These tests evaluate how well gases are being absorbed into your blood from
your lungs. Gas diffusion tests include:
Body plethysmography may be
used to measure:
Inhalation challenge tests are done to measure the
response of your airways to substances that may be causing
asthma or wheezing. These tests are also called
inhalation testing, increasing amounts of a substance are inhaled through a
nebulizer, a device that uses a face mask or mouthpiece to deliver the
substance in a fine mist (aerosol). Sometimes, increasing amounts of methacholine or mannitol may be inhaled through the nebulizer. Spirometry
readings are taken to evaluate lung function before, during, and after inhaling
In rare cases, a
bronchospasm can occur with inhalation challenge
testing. You will be closely monitored during and after the test.
Exercise stress tests
evaluate the effect of exercise on lung function tests. Spirometry readings are
done after exercise and then again at rest.
washout test is done to check lung function in people with cystic fibrosis. For
this test, you breathe air that contains a tracer gas through a tube. Then you
breathe regular air while the amount of tracer gas you exhale is monitored.
Test results are reported as a lung clearance index (LCI). A high LCI value
means that the lungs are not working well.
Lung function results are measured directly in some
tests and are calculated in others. No single test can determine all of the
lung function values, so more than one type of test may be done. Some of the
tests may be repeated after you inhale medicine that enlarges your airways
Lung function tests are done to:
Tell your doctor if you:
Do not eat a heavy meal just before this test because a
full stomach may prevent your lungs from fully expanding. You should not smoke
or exercise vigorously for 6 hours before the test. On the day of the test,
wear loose clothing that does not restrict your breathing in any way. You
should also avoid food or drinks that have caffeine because it can cause your
airways to relax and allow more air than usual to pass through.
you have dentures, wear them during the test to help you form a tight seal
around the mouthpiece of the spirometer.
Lung function tests are usually done in
special exam rooms that have all of the lung function measuring devices. The
test is usually done by a specially trained
respiratory therapist or technician. For most of the
lung function tests, you will wear a nose clip to make sure that no air passes
in or out of your nose during the test. You then will be asked to breathe into
a mouthpiece connected to a recording device.
The exact procedure
is different for each type of test. For example, you may be asked to inhale as
deeply as possible and then to exhale as fast and as hard as possible. You also
may be asked to breathe in and out as deeply and rapidly as possible for 15
seconds. Some tests may be repeated after you have inhaled a spray containing
medicine that expands the airways in your lungs (bronchodilator). You may be
asked to breathe a special mixture of gases, such as 100% oxygen, a mixture of
helium and air, or a mixture of carbon monoxide and air. Sometimes a sample of
blood may be taken from an artery in your wrist to measure blood gases.
If you have body plethysmography, you will be asked to sit inside a small
enclosure similar to a telephone booth, with windows that allow you to see out.
The booth measures small changes in pressure that occur as you breathe.
The accuracy of the tests depends on your ability to follow all of the
instructions. The therapist may strongly encourage you to breathe deeply during
some of the tests to get the best results.
The testing may take
from 5 to 30 minutes, depending upon how many tests are done.
If you have an arterial blood gas test,
you may feel some pain from the needle used to collect the blood. The other
lung function tests are usually painless. Some of the tests may be tiring for
people who have a lung disease.
You may cough or feel lightheaded
after breathing in or out rapidly, but you will be given a chance to rest
between tests. You may find it uncomfortable to wear the nose clip. Breathing
through the mouthpiece for a long period of time may be uncomfortable.
If you have body plethysmography, you may feel uncomfortable in the
airtight plethysmograph booth. But the therapist will be nearby during the test
to open the door if you feel too uncomfortable.
If you are given
breathing medicine, it may cause you to shake or may increase your heart rate.
If you feel any chest pain or discomfort, tell the therapist right away.
Lung function tests present little or no risk to
a healthy person. If you have a serious heart or lung condition, discuss your
risks with your doctor.
Lung function tests (also called pulmonary
function tests, or PFTs) check how well your lungs work. The normal value
ranges for lung function tests will be adjusted for your age, height, sex, and
sometimes weight and race. Results are often expressed in terms of a percentage
of the expected value. Most test results are available right away.
Test results are within the normal ranges
for a person with healthy lungs.
Test results are outside of the normal
range for a person with healthy lungs. This may mean that some kind of lung
disease is present. There are two main types of lung disease that can be found
with lung function tests: obstructive and restrictive.
In obstructive lung conditions, the
airways are narrowed, usually causing an increase in the time it takes to empty
the lungs. Obstructive lung disease can be caused by conditions such as
bronchitis, infection (which produces inflammation),
Forced vital capacity (FVC)
Normal or lower than predicted value
Forced expiratory volume
FEV1 divided by FVC
Forced expiratory flow 25% to 75%
Peak expiratory flow (PEF)
Maximum voluntary ventilation (MVV)
Slow vital capacity (SVC)
Normal or lower
Total lung capacity (TLC)
Normal or higher
Functional residual capacity (FRC)
Residual volume (RV)
Expiratory reserve volume (ERV)
RV divided by TLC ratio
FEV1 often increases after using medicine that expands
the airways in people with reversible obstructive disease like asthma.
In restrictive lung conditions,
there is a loss of lung tissue, a decrease in the lungs' ability to expand, or
a decrease in the lungs' ability to transfer oxygen to the blood (or carbon
dioxide out of the blood). Restrictive lung disease can be caused by conditions
or sarcoidosis. Other restrictive conditions
include some chest injuries, being very overweight (obesity),
pregnancy, and loss of lung tissue due to surgery.
Lower than predicted value
Total lung capacity (TLC)
Normal, lower, or higher
Reasons you may not be able to
have the test or why the results may not be helpful include:
Other Works Consulted
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Gustafsson PM, et al. (2008). Multiple-breath inert
gas washout and spirometry versus structural lung disease in cystic fibrosis.
Thorax, 63(2): 129–134.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Current as of:
April 25, 2013
E. Gregory Thompson, MD - Internal Medicine & Mark A. Rasmus, MD - Pulmonology, Critical Care Medicine, Sleep Medicine
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