Diffusing Capacity for Carbon Monoxide (DLCO, Transfer Factor)

Norm of Diffusing Capacity for Carbon Monoxide (DLCO, Transfer Factor)

The predicted values are based on prediction equations calculated according to gender, age, height, weight, and hemoglobin level. Results are considered abnormal if they are less than 80% of the predicted values. The average normal for resting subjects by the single-breath and steady-state methods is 25 mL/min/mm Hg.


Usage of Diffusing Capacity for Carbon Monoxide (DLCO, Transfer Factor)

Identify and monitor the course of parenchymal lung disease processes and pulmonary hypertension in scleroderma; monitor for pulmonary drug toxicity; distinguish chronic bronchitis (normal DLCO) from emphysema (low DLCO); distinguish interstitial fibrosis from pleural fibrosis.
Asthma, alveolar hemorrhage, polycythemia. Diseases or conditions associated with increased pulmonary blood flow such as left-to-right shunts, tachycardia, and exercise. Medications include inhaled budesonide corticosteroid.
Acute myocardial infarction, alveolar fibrosis (associated with sarcoidosis, asbestosis, berylliosis, ex-smokers with asthma and COPD, pneumoconiosis in coal miners, idiopathic pulmonary fibrosis, O2 toxicity, or silicosis), asbestosis, bone marrow transplant following total body irradiation, bronchiolitis obliterans with organizing pneumonia, diseases associated with anemia (such as chronic renal failure), histiocytosis X, lung resection, metal fume fever, mitral stenosis, mixed connective tissue diseases (dermatomyositis, inflammatory bowel disease, polymyositis, rheumatoid arthritis, Wegener's granulomatosis), obstructive lung diseases (emphysema, cystic fibrosis), parenchymal loss or replacement, pneumonia, posture of upright position, primary pulmonary hypertension, pulmonary edema, pulmonary emboli, restrictive lung disease, space-occupying lesions, systemic disease with pulmonary involvement (progressive systemic sclerosis, scleroderma, systemic lupus erythematosus). Drugs include amiodarone and bleomycin affecting the alveolocapillary membrane, marijuana smoking, acute and chronic ethyl alcohol ingestion, freebasing cocaine, cigarette smoking.


Description of Diffusing Capacity for Carbon Monoxide (DLCO, Transfer Factor)

Carbon monoxide (CO) is a gas that is readily taken from the alveolus and bound to hemoglobin (Hb) in pulmonary capillary blood. The diffusing capacity rate of the lung provides a measure of the lung's gas exchange mechanism. It assesses the amount of functioning pulmonary capillary bed in contact with functioning alveoli. Therefore it can provide useful information on gas-exchange properties of the lung. Thus transport or flow or uptake of carbon monoxide is a unique way to noninvasively determine the ability of the alveolar capillary membrane to transport oxygen into the blood. It is reported in cubic centimeters (of CO) per minute per millimeters of Hg or millimoles (of CO) per minute per kilopascals at 0 degrees C, 760 mm Hg, dry (i.e., STPD). There are several methods for determining the DLCO. The two most commonly used in the clinical setting are the steady-state technique and the single-breath technique.
Comparison of Steady-State and Single-Breath Methods for Determination of DLCO

Steady State
Single Breath
Generally easier for the subject to perform because no special breathing maneuvers are required. Far less susceptible to development of CO back-pressure and to effects of V/Q abnormalities.
Adaptable to use during exercise and other applications where breath holding is not feasible. Tends to be more reproducible.
Generally yields higher values (than steady-state methods) in a given subject.


Professional Considerations of Diffusing Capacity for Carbon Monoxide (DLCO, Transfer Factor)
Consent form NOT required.

  1. Assess medication record for recent analgesic that may depress respiratory function.
  2. Bronchodilators and intermittent positive-pressure breathing therapy may be withheld before the tests.
  3. The client should wear loose-fitting and comfortable clothing the day of the test.
  4. Document the client's age, gender, height, and weight on the test requisition.
  5. Dentures should not be removed.
  6. See Client and Family Teaching.



  1. The equipment used for this test consists of a sample pump and bag, a calibrated spirometer of test gas, and both a helium analyzer and a carbon monoxide analyzer.
  2. The client is positioned sitting upright with feet on the floor.
  3. A nose clip is applied to ensure consistent air flow through the mouth.
  4. Single-breath maneuver:
    • a. The client exhales completely, rapidly inhales from the spirometer to reach maximum capacity, and then holds his or her breath for 10 seconds.
    • b. Upon exhalation, 0.5–1.0 liter of exhaled air is collected and analyzed for helium and carbon monoxide.
    • c. The test is repeated after 4 minutes.
    • d. Note: Variations of this test have been published, with a second method measuring DLCO on inhalation, breath holding, and exhalation. A third method is designed for clients who cannot hold their breath for 10 seconds or achieve an adequate flow rate and is based on a slow, submaximal breath and requires different equipment.
  5. Steady-state method:
    • a. The client is instructed to breathe in and out through the mouthpiece while exercise is done or other maneuvers are carried out; measurements are taken.


Postprocedure Care

  1. Resume all medications including bronchodilators and intermittent positive-pressure breathing therapy.
  2. Test results are normally available within 30 minutes.


Client and Family Teaching

  1. Teach proper breathing technique for the test.
  2. The procedure takes approximately 20 minutes.
  3. Refrain from smoking or eating a heavy meal for 3–4 hours before the test.
  4. Refrain from drinking alcohol for 24 hours before the test.


Factors That Affect Results

  1. Reasonable airway mechanics, lung volumes, and client cooperation are required for accurate measurements.
  2. An inadequate seal around the mouthpiece invalidates the results.
  3. A supine body position increases DLCO.
  4. Exercise increases diffusing capacity.
  5. Gastric distention, hypoxia, narcotics, sedatives, and pregnancy may alter the results.
  6. Bronchodilators administered before the tests may obscure true pulmonary function.
  7. Results are adjusted for high or low hemoglobin (Hb) levels using the following equation:
  8. Single-breath method results are invalidated and reported with anecdotal notation for any of the following reasons:
    • a. Inspired vital capacity (VC) <90% of highest historical VC.
    • b. Client is unable to hold breath at least 9 seconds or holds longer than 11 seconds.
    • c. Client inspires too slowly (such as longer than 2.5–4 seconds).
  9. Females have lower diffusing capacity for carbon monoxide relative to body size.


Other Data

  1. Diffusion capacity for carbon monoxide is routinely performed in a pulmonary function laboratory.
  2. Proper interpretation of results needs to account for inherent assumptions regarding CO distribution and timing procedures.
  3. The abbreviation for the single-breath method is DLCOSB.
  4. A DLCO value of at least 70% predicts low post-pneumonectomy complications.
  5. Decreasing DLCO is an excellent predictor of subsequent development of isolated PHT as a late stage complication in limited cutaneous scleroderma.