This test involves measuring the partial pressure difference between inspired and expired carbon monoxide. It relies on the strong affinity and large absorption capacity of erythrocytes for carbon monoxide and thus demonstrates gas uptake by the capillaries that are less dependent on cardiac output. The measurement of DLCO is affected by atmospheric pressure and/or altitude and correction factors can be calculated. Expected DLCO is also affected by the amount of hemoglobin, age and sex.
Factors affecting DLCO
DLCO is decreased in any condition which affects the effective alveolar surface area:
Amiodarone high cumulative dose; more than 400 milligrams per day
However, many modern devices compensates for the hemoglobin value of the patient (taken by blood test), and excludes it as a factor in the DLCO interpretation.
Factors that can increase the DLCO include polycythaemia, asthma (can also have normal DLCO) and increased pulmonary blood volume as occurs in exercise. Other factors are left to right intracardiac shunting, and alveolar hemorrhage.
Factors affected by DLCO
A DLCO of less than 60% predicted portends a poor prognosis for lung cancer resection. FEV1 is of lesser prognostic value for lung resection survival.
^Hughes J, Bates D (2003). "Historical review: the carbon monoxide diffusing capacity (DLCO) and its membrane (DM) and red cell (Theta.Vc) components". Respir Physiol Neurobiol138 (2-3): 115–42. doi:10.1016/j.resp.2003.08.004. PMID14609505.
^Sue DY, Oren A, Hansen JE & Wasserman K (1987). Diffusing capacity for carbon monoxide as a predictor of gas exchange during exercise. N. Engl. J. Med., 316(21):1301-1306.
^Diffusion lung capacity for carbon monoxide (DLCO) is an independent prognostic factor for long-term survival after curative lung resection for cancer (p n/a) Michael J. Liptay, Sanjib Basu, Michael C. Hoaglin, Neil Freedman, L. Penfield Faber, William H. Warren, Zane T. Hammoud, Anthony W. Kim. Journal of Surgical Oncology. Published Online: Oct 1 2009 8:20AM doi:10.1002/jso.21407