Lung Diffusion Capacity

Medically Reviewed By William C. Lloyd III, MD, FACS

What is lung diffusion capacity?

Lung diffusion capacity is a simple, painless test to determine how well oxygen moves or diffuses into your bloodstream from your lungs. Doctors use lung diffusion capacity to diagnose and monitor conditions that affect the lungs’ ability to transfer oxygen into the bloodstream. Conditions include emphysema, cystic fibrosis, and pulmonary embolism (blood clot in the lungs).

Lung diffusion capacity is only one method of diagnosing and monitoring respiratory diseases. Discuss all of your testing options with your doctor to understand which options are right for you.

Other procedures that may be performed

Lung diffusion capacity is a type of pulmonary or lung function test. Your doctor will may perform one or more other pulmonary function tests to diagnose and monitor your respiratory disease, disorder or condition. Other pulmonary function tests include:

  • Arterial blood gas test to measure oxygen and carbon dioxide levels and other factors in the blood

  • Body plethysmography to determine how much air is present in your lungs when you take a deep breath and how much air is left in your lungs after you exhale as much as you can. Lung diffusion capacity may be done at the same time as a body plethysmography using the same equipment.

  • Bronchoprovocation tests to measure lung function after exposure to factors that commonly trigger asthma. This includes a methacholine challenge test to help diagnose asthma.

  • Peak expiratory flow to measure the speed of exhaling and lung constriction. People with asthma use this test routinely to monitor their asthma control.

  • Pulse oximetry to measure oxygen levels in the blood

  • Spirometry to measure the rate and amount of air that you inhale and exhale

Why is lung diffusion capacity used? 

Your doctor may recommend lung diffusion capacity testing to diagnose or monitor diseases and conditions that affect the lungs’ ability to transfer oxygen into the bloodstream. Diseases and conditions include:

  • Congenital (present at birth) lung and chest conditions including chest deformities, cystic adenomatoid malformations, pulmonary sequestrations, and congenital lobular emphysema

  • Cystic fibrosis, a genetic disorder that causes thick, sticky mucus build-up in the lungs and other organs

  • Emphysema, a chronic disease in which the alveoli (air sacs in lungs) are gradually destroyed

  • Inflammatory lung conditions including allergic alveolitis, asbestosis, sarcoidosis, and systemic lupus erythematosus (SLE)

  • Lung problems due to premature birth including pulmonary hemorrhage

  • Neuromuscular diseases including muscular dystrophy and amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease)

  • Pulmonary edema, a buildup of fluid in the alveoli (air sacs of the lungs)

  • Pulmonary embolism, a blood clot in a blood vessel of the lungs

  • Pulmonary fibrosis, lung scarring due to growth of excessive fibrous tissue in the lungs

  • Pulmonary hypertension, high blood pressure in the blood vessels of the lungs

Who performs lung diffusion capacity?

The following specialists perform or order lung diffusion capacity testing:

  • Pulmonary function technologists specialize in performing pulmonary function tests.

  • Pulmonologists and pediatric pulmonologists specialize in the medical care of people with breathing problems and diseases and conditions of the lungs. Pediatric pulmonologists further specialize in treating infants, children and adolescents.

  • Thoracic surgeons specialize in the surgical treatment of diseases of the chest, including the blood vessels, heart, lungs and esophagus. Thoracic surgeons may also be known as cardiothoracic surgeons.

  • Neonatologists specialize in caring for premature babies and full-term newborn babies with injuries, illnesses, or birth defects.

  • Congenital cardiac surgeons specialize in the surgical treatment of heart defects present at birth.

How is lung diffusion capacity performed?

Your lung diffusion capacity will be performed in a hospital. The test takes 15-20 minutes and generally involves these steps: 

  1. You will loosen any tight or restrictive clothing.

  2. The pulmonary function technologist will place a mouthpiece on you that fits tightly around your mouth and will apply nose clips.

  3. You will exhale until your lungs are empty.

  4. You will then take a deep breath and fill your lungs completely with air mixed with a very small amount of tracer gas such as carbon monoxide.

  5. You will hold your breath, generally for 10 seconds.

  6. You will rapidly exhale.

  7. Your doctor and care team will analyze the amount of tracer gas you exhale to see how much was transferred from your lungs into your bloodstream.

In some cases, lung diffusion capacity may be performed along with a body plethysmography as you sit inside a special clear cabinet or booth. This test uses a computerized pulmonary function testing system that can also perform spirometry and other pulmonary function tests. 
Will I feel pain with lung diffusion capacity?

Your comfort and relaxation is important to you and your care team. Relaxation will help obtain the most accurate test results. Undergoing a lung diffusion capacity is not painful. Tell your pulmonary function technologist if you have trouble holding your breath for about 10 seconds, are uncomfortable in any way, or have shortness of breath, wheezing, or any other symptoms during the test.

What is a normal lung diffusion capacity reading?

Lung diffusion capacity results are complex to interpret. There are also some limitations to the test because diseases and conditions outside the lungs, such as anemia and obesity, can affect the results. 

Your doctor will evaluate your results based on the limitations of the test and in relation to your age, symptoms, physical exam, medical history, and other tests. These include other pulmonary function tests and a hemoglobin or blood test. Hemoglobin is a protein in your red blood cells that carries oxygen to your organs and tissues. Your doctor will then discuss what the lung diffusion test results mean to you. 

What are the risks and potential complications of lung diffusion capacity? 

Measuring your lung diffusion capacity is generally a safe procedure without serious risks or complications.

How do I prepare for my lung diffusion capacity?

You are an important member of your own healthcare team. The steps you take before your procedure can improve your comfort and outcome.

You can prepare for a lung diffusion capacity test by:

  • Not eating a large meal before the test

  • Not smoking for six or more hours before the test

  • Stopping medication as directed by your doctor before the test. This may include not using your bronchodilator or inhaler medications. Talk to your doctor if your breathing symptoms are not well controlled or you are concerned about stopping medications briefly.

  • Wearing loose, comfortable clothing

Questions to ask your doctor

Having a lung diffusion capacity test can be stressful. It is common for patients to forget some of their questions during a doctor’s visit. You may also think of other questions after your appointment or after you leave the hospital. Contact your doctor with concerns and questions before your procedure and between appointments. 

It is also a good idea to bring a list of questions to your appointments. Questions can include:

  • Why do I need a lung diffusion capacity test? What are the other options for diagnosing and monitoring my condition?

  • Who will perform my lung diffusion capacity? Is this person a certified pulmonary function technologist?

  • How should I take my medications before and after my lung diffusion capacity test?

  • When and how can I expect to get my results?

  • When should I follow up with you?

  • How should I contact you? Ask for numbers to call during and after regular hours.

What can I expect after my lung diffusion capacity?

Knowing what to expect after a lung diffusion capacity test can help you get back to your everyday life as soon as possible.

How will I feel after my lung diffusion capacity?

You should be breathing normally after your lung diffusion capacity and not feel any ill effects of the test. Tell your doctor or pulmonary function technologist if you are dizzy, short of breath, or have any other symptoms. 

When should I call my doctor?

You should keep your follow-up appointments after lung diffusion capacity. Contact your doctor if you have any concerns between appointments. Seek emergency medical care or call 911 if shortness of breath or other breathing problems are getting worse quickly.

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  1. 1.0 What is a PFT Test? Lung Diffusing Capacity. Morgan Scientific, Inc. http://www.morgansci.com/pulmonary-function-solutions/1.0-introduction-what-is-a-pft-test/.
  2. Diffusing capacity for carbon monoxide. Wolters Kluwer Health. http://www.uptodate.com/contents/diffusing-capacity-for-carbon-monoxide.
  3. Lung Diffusing Capacity. Karger. http://content.karger.com/ProdukteDB/produkte.asp?Doi=83533.
  4. Lung Diffusion Capacity Testing (DLCO). National Jewish Health. http://www.nationaljewish.org/programs/tests/pulmonary-physiology/pulmonary-function/lung-diffusion-....
  5. Pulmonary Function Testing: Diffusing Capacity. Cleveland Clinic Center for Continuing Education. http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/pulmonary/pulmonary-function-testi....
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Jan 25
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