Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate, Inc. and/or its affiliates. All Rights Reserved.

Diffusing capacity for carbon monoxide

Meredith C McCormack, MD, MHS
Section Editor
James K Stoller, MD, MS
Deputy Editor
Helen Hollingsworth, MD


A test of the diffusing capacity of the lungs for carbon monoxide (DLCO, also known as transfer factor for carbon monoxide or TLCO), is one of the most clinically valuable tests of lung function. The technique was first described 100 years ago [1-3] and applied in clinical settings many decades later [4-6]. The DLCO measures the ability of the lungs to transfer gas from inhaled air to the red blood cells in pulmonary capillaries. The DLCO test is convenient and easy for the patient to perform. The ten seconds of breathholding required for the DLCO maneuver is easier for most patients to perform than the forced exhalation required for spirometry.

Standards for DLCO instruments, performance of the test, and calculation of the results were initially published by the American Thoracic Society in 1987, and updated by the American Thoracic Society and European Respiratory Society in 2005 and in 2017 [7-9]. The indications for DLCO measurement and the interpretation of the results will be discussed here. The use of other pulmonary function tests in the evaluation of respiratory disease in adults and children is discussed separately. (See "Office spirometry" and "Overview of pulmonary function testing in adults" and "Overview of pulmonary function testing in children".)


DLCO – The diffusing capacity for carbon monoxide (DLCO) is also known as the transfer factor for carbon monoxide or TLCO. It is a measure of the conductance of gas transfer from inspired gas to the red blood cells.

VA – The alveolar volume (VA) can be considered the number of contributing alveolar units and is measured during the single breath DLCO by use of a tracer gas (eg, helium).

KCO – The carbon monoxide transfer coefficient (KCO is approximately kCO/barometric pressure in mL/minute/ mmHg/L) is often written as DLCO/VA. It is an index of the efficiency of alveolar transfer of carbon monoxide.

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:

Subscribers log in here

Literature review current through: Nov 2017. | This topic last updated: Nov 27, 2017.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
  1. Morrell MJ. One hundred years of pulmonary function testing: a perspective on 'The diffusion of gases through the lungs of man' by Marie Krogh. J Physiol 2015; 593:351.
  2. Hughes JM, Borland CD. The centenary (2015) of the transfer factor for carbon monoxide (T(LCO)): Marie Krogh's legacy. Thorax 2015; 70:391.
  3. Krogh M. The diffusion of gases through the lungs of man. J Physiol 1915; 49:271.
  4. BLAKEMORE WS, FORSTER RE, MORTON JW, OGILVIE CM. A standardized breath holding technique for the clinical measurement of the diffusing capacity of the lung for carbon monoxide. J Clin Invest 1957; 36:1.
  5. ROUGHTON FJ, FORSTER RE. Relative importance of diffusion and chemical reaction rates in determining rate of exchange of gases in the human lung, with special reference to true diffusing capacity of pulmonary membrane and volume of blood in the lung capillaries. J Appl Physiol 1957; 11:290.
  6. JONES RS, MEADE F. A theoretical and experimental analysis of anomalies in the estimation of pulmonary diffusing capacity by the single breath method. Q J Exp Physiol Cogn Med Sci 1961; 46:131.
  7. Single breath carbon monoxide diffusing capacity (transfer factor). Recommendations for a standard technique. Statement of the American Thoracic Society. Am Rev Respir Dis 1987; 136:1299.
  8. Macintyre N, Crapo RO, Viegi G, et al. Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J 2005; 26:720.
  9. Graham BL, Brusasco V, Burgos F, et al. 2017 ERS/ATS standards for single-breath carbon monoxide uptake in the lung. Eur Respir J 2017; 49.
  10. Crapo RO, Jensen RL, Wanger JS. Single-breath carbon monoxide diffusing capacity. Clin Chest Med 2001; 22:637.
  11. Morrison NJ, Abboud RT, Ramadan F, et al. Comparison of single breath carbon monoxide diffusing capacity and pressure-volume curves in detecting emphysema. Am Rev Respir Dis 1989; 139:1179.
  12. Gould GA, Redpath AT, Ryan M, et al. Lung CT density correlates with measurements of airflow limitation and the diffusing capacity. Eur Respir J 1991; 4:141.
  13. Gevenois PA, De Vuyst P, de Maertelaer V, et al. Comparison of computed density and microscopic morphometry in pulmonary emphysema. Am J Respir Crit Care Med 1996; 154:187.
  14. Saydain G, Beck KC, Decker PA, et al. Clinical significance of elevated diffusing capacity. Chest 2004; 125:446.
  15. Merkus PJ, Govaere ES, Hop WH, et al. Preserved diffusion capacity in children with cystic fibrosis. Pediatr Pulmonol 2004; 37:56.
  16. Espiritu JD, Ruppel G, Shrestha Y, Kleinhenz ME. The diffusing capacity in adult cystic fibrosis. Respir Med 2003; 97:606.
  17. Zompatori M, Calabrò E, Chetta A, et al. [Chronic hypersensitivity pneumonitis or idiopathic pulmonary fibrosis? Diagnostic role of high resolution Computed Tomography (HRCT)]. Radiol Med 2003; 106:135.
  18. Watters LC, King TE, Schwarz MI, et al. A clinical, radiographic, and physiologic scoring system for the longitudinal assessment of patients with idiopathic pulmonary fibrosis. Am Rev Respir Dis 1986; 133:97.
  19. do Pico GA, Wiley AL Jr, Rao P, Dickie HA. Pulmonary reaction to upper mantle radiation therapy for Hodgkin's disease. Chest 1979; 75:688.
  20. Theuws JC, Muller SH, Seppenwoolde Y, et al. Effect of radiotherapy and chemotherapy on pulmonary function after treatment for breast cancer and lymphoma: A follow-up study. J Clin Oncol 1999; 17:3091.
  21. Luursema PB, Star-Kroesen MA, van der Mark TW, et al. Bleomycin-induced changes in the carbon monoxide transfer factor of the lungs and its components. Am Rev Respir Dis 1983; 128:880.
  22. Crawford SW, Pepe M, Lin D, et al. Abnormalities of pulmonary function tests after marrow transplantation predict nonrelapse mortality. Am J Respir Crit Care Med 1995; 152:690.
  23. Ewert R, Opitz C, Wensel R, et al. Abnormalities of pulmonary diffusion capacity in long-term survivors after kidney transplantation. Chest 2002; 122:639.
  24. Mitchell DM, Fleming J, Pinching AJ, et al. Pulmonary function in human immunodeficiency virus infection. A prospective 18-month study of serial lung function in 474 patients. Am Rev Respir Dis 1992; 146:745.
  25. Nieman RB, Fleming J, Coker RJ, et al. Reduced carbon monoxide transfer factor (TLCO) in human immunodeficiency virus type I (HIV-I) infection as a predictor for faster progression to AIDS. Thorax 1993; 48:481.
  26. Schachter LM, Dixon J, Pierce RJ, O'Brien P. Severe gastroesophageal reflux is associated with reduced carbon monoxide diffusing capacity. Chest 2003; 123:1932.
  27. Schwartz DA, Van Fossen DS, Davis CS, et al. Determinants of progression in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 1994; 149:444.
  28. Steenhuis LH, Groen HJ, Koëter GH, van der Mark TW. Diffusion capacity and haemodynamics in primary and chronic thromboembolic pulmonary hypertension. Eur Respir J 2000; 16:276.
  29. Fernandez-Bonetti P, Lupi-Herrera E, Martinez-Guerra ML, et al. Peripheral airways obstruction in idiopathic pulmonary artery hypertension (primary). Chest 1983; 83:732.
  30. Tashkin DP, Clements PJ, Wright RS, et al. Interrelationships between pulmonary and extrapulmonary involvement in systemic sclerosis. A longitudinal analysis. Chest 1994; 105:489.
  31. Hills EA, Geary M. Membrane diffusing capacity and pulmonary capillary volume in rheumatoid disease. Thorax 1980; 35:851.
  32. Songür N, Songür Y, Tüzün M, et al. Pulmonary function tests and high-resolution CT in the detection of pulmonary involvement in inflammatory bowel disease. J Clin Gastroenterol 2003; 37:292.
  33. Herrlinger KR, Noftz MK, Dalhoff K, et al. Alterations in pulmonary function in inflammatory bowel disease are frequent and persist during remission. Am J Gastroenterol 2002; 97:377.
  34. Wang JS. Relationship of carbon monoxide pulmonary diffusing capacity to postoperative cardiopulmonary complications in patients undergoing pneumonectomy. Kaohsiung J Med Sci 2003; 19:437.
  35. Datta D, Lahiri B. Preoperative evaluation of patients undergoing lung resection surgery. Chest 2003; 123:2096.
  36. Beckles MA, Spiro SG, Colice GL, et al. The physiologic evaluation of patients with lung cancer being considered for resectional surgery. Chest 2003; 123:105S.
  37. Iwasaki A, Yosinaga Y, Kawahara K, Shirakusa T. Evaluation of lung volume reduction surgery (LVRS) based on long-term survival rate analysis. Thorac Cardiovasc Surg 2003; 51:277.
  38. National Emphysema Treatment Trial Research Group, Fishman A, Fessler H, et al. Patients at high risk of death after lung-volume-reduction surgery. N Engl J Med 2001; 345:1075.
  39. Sue DY, Oren A, Hansen JE, Wasserman K. Diffusing capacity for carbon monoxide as a predictor of gas exchange during exercise. N Engl J Med 1987; 316:1301.
  40. Hadeli KO, Siegel EM, Sherrill DL, et al. Predictors of oxygen desaturation during submaximal exercise in 8,000 patients. Chest 2001; 120:88.
  41. Mohsenifar Z, Lee SM, Diaz P, et al. Single-breath diffusing capacity of the lung for carbon monoxide: a predictor of PaO2, maximum work rate, and walking distance in patients with emphysema. Chest 2003; 123:1394.
  42. Baldi S, Fracchia C, Bruschi C, et al. Effect of bronchodilatation on single breath pulmonary uptake of carbon monoxide in chronic obstructive pulmonary disease. Int J Chron Obstruct Pulmon Dis 2006; 1:477.
  43. Yang J, Stanton J, Wang L, et al. Effect of salbutamol on the measurement of single-breath diffusing capacity. Respirology 2013; 18:1223.
  44. Jensen RL, Crapo RO. Diffusing capacity: how to get it right. Respir Care 2003; 48:777.
  45. Hughes JM, Pride NB. Examination of the carbon monoxide diffusing capacity (DL(CO)) in relation to its KCO and VA components. Am J Respir Crit Care Med 2012; 186:132.
  46. Sansores RH, Abboud RT, Kennell C, Haynes N. The effect of menstruation on the pulmonary carbon monoxide diffusing capacity. Am J Respir Crit Care Med 1995; 152:381.
  47. Sansores RH, Pare PD, Abboud RT. Acute effect of cigarette smoking on the carbon monoxide diffusing capacity of the lung. Am Rev Respir Dis 1992; 146:951.
  48. Graham BL, Mink JT, Cotton DJ. Effects of increasing carboxyhemoglobin on the single breath carbon monoxide diffusing capacity. Am J Respir Crit Care Med 2002; 165:1504.
  49. Sansores RH, Pare P, Abboud RT. Effect of smoking cessation on pulmonary carbon monoxide diffusing capacity and capillary blood volume. Am Rev Respir Dis 1992; 146:959.
  50. Crapo RO, Morris AH. Standardized single breath normal values for carbon monoxide diffusing capacity. Am Rev Respir Dis 1981; 123:185.
  51. Johnson DC. Importance of adjusting carbon monoxide diffusing capacity (DLCO) and carbon monoxide transfer coefficient (KCO) for alveolar volume. Respir Med 2000; 94:28.
  52. Fitting JW. Transfer factor for carbon monoxide: a glance behind the scene. Swiss Med Wkly 2004; 134:413.
  53. Kaminsky DA, Whitman T, Callas PW. DLCO versus DLCO/VA as predictors of pulmonary gas exchange. Respir Med 2007; 101:989.
  54. McGRATH MW, THOMSON ML. The effect of age, body size and lung volume change on alveolar-capillary permeability and diffusing capacity in man. J Physiol 1959; 146:572.
  55. Miller MR. Does the use of per cent of predicted have any evidence base? Eur Respir J 2015; 45:322.
  56. Miller A, Thornton JC, Warshaw R, et al. 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. Am Rev Respir Dis 1983; 127:270.
  57. Rijcken B, Schouten JP, Xu X, et al. Airway hyperresponsiveness to histamine associated with accelerated decline in FEV1. Am J Respir Crit Care Med 1995; 151:1377.
  58. Kitaichi M, Nishimura K, Itoh H, Izumi T. Pulmonary lymphangioleiomyomatosis: a report of 46 patients including a clinicopathologic study of prognostic factors. Am J Respir Crit Care Med 1995; 151:527.
  59. Hart N, Cramer D, Ward SP, et al. Effect of pattern and severity of respiratory muscle weakness on carbon monoxide gas transfer and lung volumes. Eur Respir J 2002; 20:996.
  60. Whyte MK, Hughes JM, Peters AM, et al. Analysis of intrapulmonary right to left shunt in the hepatopulmonary syndrome. J Hepatol 1998; 29:85.
  61. Rodríguez-Roisin R, Krowka MJ. Hepatopulmonary syndrome--a liver-induced lung vascular disorder. N Engl J Med 2008; 358:2378.
  62. Coulter TD, Stoller JK. What causes an elevated diffusing capacity? Respir Care 2000; 45:531.
  63. Stewart RI. Carbon monoxide diffusing capacity in asthmatic patients with mild airflow limitation. Chest 1988; 94:332.
  64. Kanengiser LC, Rapoport DM, Epstein H, Goldring RM. Volume adjustment of mechanics and diffusion in interstitial lung disease. Lack of clinical relevance. Chest 1989; 96:1036.
  65. Drummond MB, Schwartz PF, Duggan WT, et al. Intersession variability in single-breath diffusing capacity in diabetics without overt lung disease. Am J Respir Crit Care Med 2008; 178:225.
  66. Mushtaq M, Hayton R, Watts T, et al. An audit of pulmonary function laboratories in the West Midlands. Respir Med 1995; 89:263.
  67. Hegewald MJ, Markewitz BA, Wilson EL, et al. Single-breath diffusing capacity for carbon monoxide instrument accuracy across 3 health systems. Respir Care 2015; 60:430.
  68. Hathaway EH, Tashkin DP, Simmons MS. Intraindividual variability in serial measurements of DLCO and alveolar volume over one year in eight healthy subjects using three independent measuring systems. Am Rev Respir Dis 1989; 140:1818.
  69. Robson AG, Innes JA. Short term variability of single breath carbon monoxide transfer factor. Thorax 2001; 56:358.
  70. Jensen RL, Teeter JG, England RD, et al. Instrument accuracy and reproducibility in measurements of pulmonary function. Chest 2007; 132:388.
  71. Jensen RL, Teeter JG, England RD, et al. Sources of long-term variability in measurements of lung function: implications for interpretation and clinical trial design. Chest 2007; 132:396.
  72. Stanojevic S, Graham BL, Cooper BG, et al. Official ERS technical standards: Global Lung Function Initiative reference values for the carbon monoxide transfer factor for Caucasians. Eur Respir J 2017; 50.
  73. Huang YC, Macintyre NR. Real-time gas analysis improves the measurement of single-breath diffusing capacity. Am Rev Respir Dis 1992; 146:946.
  74. Guenard H, Varene N, Vaida P. Determination of lung capillary blood volume and membrane diffusing capacity in man by the measurements of NO and CO transfer. Respir Physiol 1987; 70:113.
  75. Borland CD, Higenbottam TW. A simultaneous single breath measurement of pulmonary diffusing capacity with nitric oxide and carbon monoxide. Eur Respir J 1989; 2:56.
  76. Glénet SN, De Bisschop C, Vargas F, Guénard HJ. Deciphering the nitric oxide to carbon monoxide lung transfer ratio: physiological implications. J Physiol 2007; 582:767.