Lung Diffusion Capacity Testing (DLCO) Make an Appointment Ask a Question Refer Patient Reviewed by Amy Olson and George Zeman (September 01, 2015) This test measures how well gases (oxygen) move through the lung and into the bloodstream. A technologist will instruct you on how to perform the test and coach and encourage you to do your best. This information has been approved by George Zeman BS, RRT, CPFT and Amy L. Olson, MD, MSPH (September 2015).