Lung Function Tests

Pulmonary Function Tests

Results

Lung function tests (also called pulmonary function tests, or PFTs) evaluate 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.

Normal

Test results are within the normal ranges for a person with healthy lungs.

Abnormal

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.

Obstructive

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 emphysema, bronchitis, infection (which produces inflammation), and asthma.

Lung function values in obstructive disease

Lung function test	Result as predicted for age, height, sex, weight, or race
Forced vital capacity (FVC)	Normal or lower than predicted value
Forced expiratory volume (FEV1)	Lower
FEV1 divided by FVC	Lower
Forced expiratory flow 25% to 75%	Lower
Peak expiratory flow (PEF)	Lower
Maximum voluntary ventilation (MVV)	Lower
Slow vital capacity (SVC)	Normal or lower
Total lung capacity (TLC) (VT)	Normal or higher
Functional residual capacity (FRC)	Higher
Residual volume (RV)	Higher
Expiratory reserve volume (ERV)	Normal or lower
RV divided by TLC ratio	Higher

FEV1 often increases after using medicine that expands the airways in people with reversible obstructive disease like asthma.

Restrictive

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 such as pneumonia, lung cancer, scleroderma, pulmonary fibrosis, sarcoidosis, or multiple sclerosis. Other restrictive conditions include some chest injuries, being very overweight (obesity), pregnancy, and loss of lung tissue due to surgery.

Lung function values in restrictive disease

Lung function test	Result as predicted for age, height, sex, weight, or race
Forced vital capacity (FVC)	Lower than predicted value
Forced expiratory volume (FEV1)	Normal or lower
FEV1 divided by FVC	Normal or higher
Forced expiratory flow 25% to 75%	Normal or lower
Peak expiratory flow (PEF)	Normal or lower
Maximum voluntary ventilation (MVV)	Normal or lower
Slow vital capacity (SVC)	Lower
Total lung capacity (TLC) (VT)	Lower
Functional residual capacity (FRC)	Normal or lower
Residual volume (RV)	Normal, lower, or higher
Expiratory reserve volume (ERV)	Normal or lower
RV divided by TLC ratio	Normal or higher

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Author:	Maria Essig	Last Updated: June 7, 2009
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology
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