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== Interpretation ==
The diffusing capacity (DLCO) is a test of the integrity of the alveolar-capillary surface area for gas transfer. It may be reduced in disorders that damage the alveolar walls (septa) such as emphysema, which leads to a loss of effective surface area. The DLCO is also reduced in disorders that thicken or damage the alveolar walls such as [[pulmonary fibrosis]]. The DLCO is also reduced in interstitial lung diseases such as [[hypersensitivity pneumonitis]] (e.g. [[bird fancier's lung]], [[farmer's lung]]) or dust-inhalation diseases such as [[asbestosis]]. Because the transfer of CO depends upon how much blood is present in the lung capillaries, the DLCO can be reduced due to [[anemia]] and raised in [[polycythemia]]. Some laboratories adjust or correct the DLCO for a serum hemoglobin to take into account the effect of anemia. Disorders of the pulmonary blood vessels such as [[chronic thromboembolic disease]] or [[pulmonary hypertension]] also reduce the diffusing capacity, as can any condition/disease which results in reduction in pulmonary capillary blood volume. The DLCO is not, however, a sensitive test for acute pulmonary embolism. Cigarette smokers tend to have lower DLCO, which is partly due to damage to the lungs (mild emphysema) and partly due to the retention of carbon monoxide from the cigarettes, which causes back pressure (decreasing the CO gradient). For these reasons, the DLCO is a sensitive test for disorders of the lung, but does not point toward a specific diagnosis. By calculating the dilution of the tracer gas, the test can also be used to estimate the [[total lung capacity]]. In the presence of poor gas mixing from obstructive lung disease it is used to measure the single breath total lung capacity.
== External links ==
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