CPT® Code 94729

Add-On Code

The diffusing capacity of the lungs, specifically using carbon monoxide (CO), is a critical pulmonary function test that assesses the lungs' ability to transfer gases from inhaled air into the bloodstream. This test is particularly important for evaluating the efficiency of the alveolar-capillary membrane, which is the site where gas exchange occurs. The procedure is designed to differentiate between lung restrictions caused by parenchymal diseases, which affect the lung tissue itself, and those caused by extrapulmonary factors, such as decreased cardiac output. During the test, the patient is required to exhale completely before inhaling a specific gas mixture that includes 0.3 percent carbon monoxide, 10 percent helium, 21 percent oxygen, and 68.7 percent nitrogen. This mixture is delivered through a mouthpiece connected to the diffusion capacity testing device. Once the patient reaches total lung capacity, they hold their breath for a duration of 10 seconds, allowing for optimal gas exchange. After this brief pause, the patient exhales, discarding the initial gas that remains in the conducting airways, which includes the mouth, trachea, and bronchi. The remaining exhaled gas is collected for analysis. The results of this test provide valuable insights into the lung's diffusing capacity, and the physician is responsible for reviewing these results and generating a comprehensive written report detailing the findings.