What is the difference between spirometry and a pulmonary function test (PFT)?
A spirometry test is a specific type of pulmonary function test. Spirometry measures the lungs volume (or how much) and flow (how quickly) the patient can move air into and out of their lungs. Spirometry will tell the tester if the patient has an obstruction, restriction, a mixed defect, or has normal lung flow.
Spirometry does NOT look at gas exchange and does not provide absolute lung volumes (RV, FRC, and TLC).
Diffusion capacity or transfer factor of the lung for carbon monoxide (CO) is known as a DLCO test. This measures the gas exchange and is used in conjunction with spirometry to provide a differential diagnosis. DLCO is also used to assess disease severity and is one of the best correlates of emphysema in COPD.
The final component that completes the full PFT exam is measuring absolute lung volume (RV, FRC, and TLC). This is completed by measuring body plethysmography, gas dilution, or nitrogen washout. Lung volumes are commonly used for the diagnosis of restriction. In obstructive lung disease, they are used to assess for hyperinflation. The changes in lung volumes can also be seen in a number of other clinical conditions.
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