A test of the diffusing capacity of the lungs for carbon monoxide (DLCO) is one of the most clinically valuable tests of lung function. The technique was first described 100 years ago and applied in clinical settings many decades later. The DLCO measures the ability of the lungs to transfer gas from inhaled air to the red blood cells in pulmonary capillaries. The DLCO test is convenient and easy for the patient to perform. The ten seconds of breathholding required for the DLCO maneuver is easier for most patients to perform than the forced exhalation required for Spirometry.
You breathe in (inhale) air containing a very small amount of carbon monoxide and a tracer gas, such as methane or helium. You hold your breath for 10 seconds, then rapidly blow it out (exhale). The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath. If you had a PFT (Pulmonary Function Test) you probably had this test at that time.
Normal test results depend on a person's:
- Hemoglobin (the protein in red blood cells that carries oxygen) level
Simply put, diffusion capacity is a measurement of the lung's ability to transfer gases. Those of us with diminished diffusion/DLCO experience air trapping, and although taking a breath in is easy, getting the trapped air out is not. The measurement of diffusion capacity gives important information regarding the integrity and size of the alveolar blood membrane. It measures the diffusion of gas across the alveolar membrane which is determined by the surface area and integrity of the alveolar membrane and the pulmonary vascular bed. In COPD the upper lobes tend to be damaged whereas in alpha 1 antitrypsin deficiency (genetically hereditary emphysema) the lower lobes are predominantly involved.
Results can help physicians differentiate emphysema from chronic bronchitis and asthma. Patients with emphysema have lower DLCO results, indicated by a reduced ability to take up oxygen. Such results are also important in helping to determine appropriate candidates for lung reduction surgery. Carbon monoxide levels that are 20% or less than predicted values pose a very high risk for poor survival.
Like FEV1 knowing your DLCO will help you to determine what treatments are appropriate. Understanding these tests and discussing them with your Physician and Pulmonologist empowers you to comply and/or advocate for yourself.