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COPD Assessments
Respiratory Function Testing (RFTs)

As the name implies, respiratory function tests (RFTs) measure how well the lungs are moving air in and out. They also measure how well the lungs are moving oxygen to the blood. These breathing tests use special equipment and are done by trained staff in a hospital or office setting. Most are done by blowing into a tube while you sit in a chair.

Individuals with COPD often have abnormal RFT results which suggest airway blockage and air trapping. Similar changes can be seen in some other lung conditions, such as asthma. If the lung function testing includes a diffusing capacity (DLCO) test, a low value suggests emphysema.

Many factors can affect the results of these tests. These include the current health of your lungs, the skill of the person testing you, your effort and the type of equipment used. PFTs are helpful in measuring the effects of lung medicines on lung function. They can also determine how serious are the disorders affecting the airways or other lung tissue. PFTs are also helpful when preparing for lung surgery.



A test of the diffusing capacity of the lungs for carbon monoxide (DLCO) is one of the most clinically valuable tests of lung function. Diffusing capacity (also known as transfer factor) is measured using small volumes of carbon monoxide (CO) and measures the transfer of CO across the alveolar-capillary membrane. DLCO can assist in the identification, assessment of severity and monitoring of a wide range of disease processes affecting the lung parenchyma and pulmonary vascular bed.


There are multiple clinical indications for measurement of DLCO, and there are no contraindications or adverse effects.

Indications for performing a DLCO test include:

Interpretation of DLCO Summary

Decreased DLCO

Increased DLCO