TLCO (Transfer Factor for Lung diffusion of Carbon Monoxide) is a test used to determine how well the lungs can transfer gas, such as carbon monoxide, from the air we breathe into the blood. This is one of the most important functions of the lungs, as it is crucial for our body to be able to transfer oxygen from the air into the bloodstream. The TLCO test can help doctors diagnose various lung diseases, such as COPD (Chronic Obstructive Pulmonary Disease), asthma, pulmonary fibrosis, or pulmonary embolism. During the test, the patient takes a deep breath of a mixture of gases, including a small amount of carbon monoxide, and then holds their breath for a few seconds before exhaling. From the results of the test, doctors can determine how well the lungs are functioning.