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| OtherCodes = CPT: 94720
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'''Diffusing capacity''' of the lung (D<sub>L</sub>) (also known as Transfer''transfer factor is another expression for the formerly used diffusing capacity.'') measures the transfer of gas from air in the lung, to the [[red blood cell]]s in lung blood vessels. It is part of a comprehensive series of [[pulmonary function testing|pulmonary function tests]] to determine the overall ability of the [[lung]] to transport gas into and out of the blood. D<sub>L</sub>, especially [[DLCO|D<sub>LCO</sub>]], is reduced in certain diseases of the lung and heart. D<sub>LCO</sub> measurement has been standardized according to a position paper<ref name="multiple">{{cite journal |vauthors=Macintyre N, Crapo RO, Viegi G, etal | year = 2005 | title = Standardisation of the single-breath determination of carbon monoxide uptake in the lung | journal = Eur Respir J | volume = 26 | issue = 4| pages = 720–35 | doi = 10.1183/09031936.05.00034905 | pmid = 16204605 | s2cid = 18177228 | doi-access = free }}</ref> by a task force of the [[European Respiratory Society|European Respiratory]] and [[American Thoracic Society|American Thoracic]] Societies.
In [[respiratory physiology]], the diffusing capacity has a long history of great utility, representing [[Electrical resistance and conductance|conductance]] of gas across the alveolar-capillary membrane and also takes into account factors affecting the behaviour of a given gas with hemoglobin.{{Citation needed|reason=uncited definition|date=March 2014}}
== Interpretation ==
In general, a healthy individual has a value of <math>D_{L_{CO}}</math> between 75% and 125% of the average.<ref name=uppsala>LUNGFUNKTION - Practice compendium for semester 6. Department of Medical Sciences, Clinical Physiology, Academic Hospital, Uppsala, Sweden. Retrieved 2010.</ref> However, individuals vary according to age, sex, height and a variety of other parameters. For this reason, reference values have been published, based on populations of healthy subjects<ref>{{cite journal |vauthors=Miller A, Thornton JC, Warshaw R, Anderson H, Teirstein AS, Selikoff IJ | year = 1983 | title = Single breath diffusing capacity in a representative sample of the population of Michigan, a large industrial state. Predicted values, lower limits of normal, and frequencies of abnormality by smoking history | journal = Am Rev Respir Dis | volume = 127 | issue = 3| pages = 270–7 | pmid = 6830050 | doi = 10.1164/arrd.1983.127.3.270 | doi-broken-date = 3112 DecemberJuly 20222025 }}</ref><ref>{{cite journal |vauthors=Knudson RJ, Kaltenborn WT, Knudson DE, Burrows B | year = 1987 | title = The single-breath carbon monoxide diffusing capacity. Reference equations derived from a healthy nonsmoking population and effects of hematocrit | journal = Am Rev Respir Dis | volume = 135 | issue = 4| pages = 805–11 | pmid = 3565929 | doi=10.1164/arrd.1987.135.4.805}}</ref><ref>{{cite journal |vauthors=Cotes JE, Chinn DJ, Quanjer PH, Roca J, Yernault JC | year = 1993 | title = Standardization of the measurement of transfer factor (Diffusing capacity) | journal = Eur Respir J Suppl | volume = 16 | pages = 41–52 | pmid = 8499053 | doi = 10.1183/09041950.041s1693 | s2cid = 54555111 | doi-access = free }}</ref> as well as measurements made at altitude,<ref>{{cite journal |vauthors=Crapo RO, Morris AH, Gardner RM | year = 1982 | title = Reference values for pulmonary tissue volume, membrane diffusing capacity, and pulmonary capillary blood volume | journal = Bull Eur Physiopathol Respir | volume = 18 | issue = 6| pages = 893–9 | pmid = 6927541 }}</ref> for children<ref>{{cite journal |vauthors=Koopman M, Zanen P, Kruitwagen CL, van der Ent CK, Arets HG | year = 2011 | title = Reference values for paediatric pulmonary function testing: The Utrecht dataset | journal = Respir. Med. | volume = 105 | issue = 1| pages = 15–23 |pmid=20889322 | doi=10.1016/j.rmed.2010.07.020| doi-access = free }} Erratum in ''Respir. Med.'' 2011 Dec;105(12):1970-1.</ref> and some specific population groups.<ref>{{cite journal |vauthors=Chin NK, Ng TP, Hui KP, Tan WC | date = Jun 1997 | title = Population based standards for pulmonary function in non-smoking adults in Singapore | journal = Respirology | volume = 2 | issue = 2| pages = 143–9 | pmid = 9441128 | doi=10.1111/j.1440-1843.1997.tb00070.x| s2cid = 31037816 }}</ref><ref>{{cite journal |vauthors=Piirilä P, Seikkula T, Välimäki P | year = 2007 | title = Differences between Finnish and European reference values for pulmonary diffusing capacity | journal = Int J Circumpolar Health | volume = 66 | issue = 5| pages = 449–57 | pmid = 18274210 | doi = 10.3402/ijch.v66i5.18316 | s2cid = 22302973 | doi-access = free }}</ref><ref>{{cite journal |vauthors=Ip MS, Lam WK, Lai AY, etal | title = Hong Kong Thoracic Society. Reference values of diffusing capacity of non-smoking Chinese in Hong Kong | journal = Respirology | volume = 12 | issue = 4| pages = 599–606 | doi = 10.1111/j.1440-1843.2007.01084.x | pmid = 17587430 | date=July 2007| s2cid = 5897844 }}</ref>
===Blood CO levels may not be negligible===
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