A test of the diffusing capacity of the lungs for carbon monoxide (DLCO, also known as transfer factor for carbon monoxide or TLCO), is one of the most clinically valuable tests of lung function.

How is a DLCO test performed?

Diffusing capacity (DLCO) is most commonly measured using the single-breath technique. The patient takes a full inspiration of a gas mixture containing 0.3 percent carbon monoxide and 10 percent helium (the dilution of which provides an index of lung or “alveolar” volume).

Why is DLCO test done?

A lung diffusion test is used to examine how your lungs are processing air. Along with other tests, it can help your doctor determine whether your respiratory system is working properly and efficiently. It may also be known as a diffusing capacity of the lung for carbon monoxide (DLCO) test.