Diffusing capacity of the lungs for carbon monoxide (DLCO) is also known as the transfer factor. It is a measurement to assess the lungs; ability to transfer gas from inspired air to the bloodstream across the respiratory membrane which separates air within the alveoli from blood flowing in the pulmonary capillaries.
Inhaled CO is used for this test as the tracer gas because of its high affinity for hemoglobin (200 to 250 times that of oxygen). DLCO measures uptake of CO per unit time per mm of driving pressure of CO (cc of CO/sec/mm of Hg).DLCO is used in the diagnosis of causes of breathlessness, coughing or wheezing and for screening for certain lung diseases. It is particularly useful in cases where lung parenchyma and respiratory membrane is diseases such as in case of Interstitial Lung Diseases (ILDs), Pulmonary Fibrosis and Emphysema. DLCO is used to assess the function of respiratory membrane and degree of lung damage.
Serial DLCO is helpful to understand how an underlying disease is affecting the lung function and to get information on how well a treatment is working. It is also helpful to understand whether an existing condition is getting better or worse. DLCO can also be used to evaluate the functioning of the lungs before surgery or before a strenuous, rehabilitative exercise program.