When patients undergo lung function testing, they often encounter unfamiliar terms like DLCO that can seem confusing at first. DLCO stands for Diffusing Capacity of the Lungs for Carbon Monoxide, and it measures how well oxygen moves from your lungs into your bloodstream.
This test uses a small amount of carbon monoxide to evaluate your lungs’ ability to transfer gases effectively. At Gwinnett Pulmonary, we use DLCO testing as a key tool to diagnose and monitor various lung conditions.
Unlike basic breathing tests that measure air flow, DLCO gives us specific information about how your lung tissue functions at the microscopic level. This makes it especially valuable for detecting conditions like emphysema, pulmonary fibrosis, and other diseases that affect gas exchange.
DLCO measures how well your lungs transfer carbon monoxide from inhaled air to your bloodstream. This test shows us the health of your lung’s gas exchange system and helps doctors find lung problems early.
DLCO stands for Diffusing Capacity of the Lungs for Carbon Monoxide. We also call it transfer factor for carbon monoxide or TLCO.
This pulmonary function test measures how much carbon monoxide moves from your lungs to your blood in one minute. We express the results in mL/min/mm Hg or mmol/min/kPa.
The test uses carbon monoxide because this gas binds strongly to hemoglobin in your blood. We don’t use oxygen because it doesn’t bind as well to hemoglobin.
During the test, you breathe in a small amount of carbon monoxide mixed with other gases. The amount that transfers to your blood tells us how well your lungs work.
Key components measured include:
Diffusion capacity shows how well gases move across the thin membrane between your air sacs and blood vessels. This process is vital for getting oxygen into your blood and removing carbon dioxide.
The diffusion process depends on several factors:
When your lung membrane gets thicker or damaged, diffusion capacity drops. This happens in diseases like pulmonary fibrosis or emphysema.
We use carbon monoxide because its uptake depends mainly on the membrane condition, not blood flow. This gives us a clear picture of your lung’s gas exchange ability.
Normal diffusion capacity means oxygen can easily move from your lungs to your blood. Poor diffusion capacity suggests lung damage or disease.
DLCO testing gives us information that other pulmonary function tests cannot provide. While spirometry measures airflow, DLCO measures gas exchange efficiency.
We use DLCO to:
Low DLCO values often indicate emphysema, pulmonary fibrosis, or blood vessel problems in the lungs. Values below 50% suggest high risk for oxygen problems during exercise.
Values below 40% may qualify patients for disability benefits. Very low values indicate need for oxygen therapy.
We often combine DLCO with other PFTs to get a complete picture of your lung health. This combination helps us make accurate diagnoses and create better treatment plans.
The DLCO test measures how well gas moves from the lungs into the bloodstream using a specific breathing technique with carbon monoxide. We use standardized procedures to evaluate the alveolar-capillary membrane’s ability to transfer oxygen during normal breathing.
The diffusing capacity test works by measuring how gas moves across the alveolar-capillary membrane. This thin barrier separates air in the alveoli from blood in the tiny blood vessels.
We use Fick’s law of diffusion to understand this process. Gas movement depends on several factors:
When the membrane gets thicker or damaged, less gas can pass through. We see this in diseases like pulmonary fibrosis.
If the surface area shrinks, gas exchange drops too. This happens in emphysema when alveoli get destroyed.
The test gives us a number that shows how much gas transfers per minute. We measure this in milliliters per minute per millimeter of mercury pressure.
We use carbon monoxide instead of oxygen for this test because it works better for measuring. Carbon monoxide binds very strongly to red blood cells once it crosses into the bloodstream.
Oxygen doesn’t work as well because it binds weakly to hemoglobin. Blood flow affects how much gets absorbed.
The body uses oxygen quickly. Carbon monoxide gives us cleaner results.
Its strong binding means the alveolar-capillary membrane is the main thing that limits how fast it gets absorbed. The test gas contains only 0.3% carbon monoxide.
This tiny amount is safe and won’t hurt patients. We also add a tracer gas like helium to the mixture.
This helps us measure lung volume at the same time.
Most labs use the single-breath method for the DLCO test. We connect patients to equipment through a mouthpiece and nose clip.
The test follows these steps:
We throw away the first part of the exhaled air because it comes from airways, not alveoli. Then we collect a sample for testing.
The breath-hold time is critical. We need exactly 10 seconds for accurate results.
Patients can’t smoke for at least 4 hours before testing. They also stop using oxygen for 15 minutes before we start.
We repeat the test at least twice. Results must be within 2 points of each other to be valid.
The diffusion test measures two main things that we multiply together to get the final DLCO result. Alveolar Volume (Va) shows how much lung space the test gas reaches.
We calculate this by seeing how much the helium gets diluted when it spreads through the lungs. The formula we use is: Va = Vi × (Initial Helium/Final Helium)
Carbon Monoxide Uptake Rate (Kco) measures how fast CO disappears from the alveoli during the 10-second breath hold. We compare CO levels at the start and end: Kco = natural log(Starting CO/Ending CO) ÷ time
The final DLCO result comes from: DLCO = Va × Kco
Normal results depend on age, height, sex, and race.
We compare each patient’s results to predicted normal values for people like them.
DLCO results provide crucial information about how well your lungs transfer oxygen from air into your bloodstream. The values help us identify lung diseases and track treatment progress.
We measure DLCO as a percentage of predicted normal values based on your age, height, and gender. The test shows how efficiently carbon monoxide moves from your lungs into your blood.
DLCO/VA ratio is another important measurement we use. This compares your diffusing capacity to your lung volume.
A ratio below 0.8 suggests problems with gas transfer across lung tissue. When DLCO drops, it means your lungs cannot move oxygen into your blood as well as they should.
This happens when lung tissue becomes damaged or thickened. We also look at how DLCO changes over time.
A steady decline often shows that lung disease is getting worse.
Normal DLCO values typically fall between 80% and 120% of predicted values for healthy people. Values in this range suggest good lung function.
Mildly reduced DLCO ranges from 60% to 79% of predicted. This may indicate early lung disease or mild damage to lung tissue.
Significantly reduced DLCO is below 60% of predicted. This level often points to serious lung problems that need more testing and treatment.
Some conditions can make DLCO higher than normal. These include:
Low DLCO appears in many lung diseases like pulmonary fibrosis, emphysema, and pulmonary hypertension.
DLCO results often match the symptoms you experience. Lower values usually mean more severe shortness of breath during daily activities.
When your diffusing capacity drops significantly, you may notice breathing problems with light exercise or even at rest. This happens because your lungs cannot get enough oxygen into your blood.
We use DLCO to understand why you have shortness of breath. Sometimes lung volume tests appear normal, but DLCO shows the real problem with gas exchange.
The test helps us track how your symptoms change over time. DLCO also helps us predict how well you might handle physical activity or surgery.
Several lung and blood conditions can change DLCO test results in predictable ways. Lower DLCO values often indicate problems with lung tissue or blood vessels, while higher values may signal bleeding or heart issues.
Pulmonary fibrosis causes thick scar tissue to form in the lungs. This scarring makes the walls between air sacs much thicker than normal.
When lung tissue becomes thick and stiff, oxygen cannot pass easily from the lungs into the blood. The DLCO test shows this problem clearly.
We often see reduced DLCO values in patients with:
The DLCO test can detect these conditions early. Sometimes we find low DLCO results before patients notice symptoms or breathing problems.
This early detection helps doctors start treatment sooner. It also helps us track how well treatments work over time.
Emphysema destroys the tiny air sacs in the lungs called alveoli. This damage reduces the surface area where oxygen enters the blood.
Patients with COPD often have emphysema along with chronic bronchitis. Both conditions can lower DLCO test results.
The damage happens because air sacs break down and merge together. Less lung tissue contacts blood vessels.
Gas exchange becomes less efficient. We use DLCO tests to measure how much lung damage has occurred.
Lower scores mean more severe damage to lung tissue. Unlike some COPD damage, emphysema changes are permanent.
However, proper treatment can help protect remaining healthy lung tissue.
Anemia means having fewer red blood cells than normal. Since red blood cells carry oxygen, this affects DLCO test results.
Low hemoglobin levels cause lower DLCO values even when lungs are healthy. The test uses carbon monoxide, which binds to hemoglobin just like oxygen does.
We adjust DLCO results based on hemoglobin levels to get accurate readings. This helps us tell the difference between lung problems and blood problems.
Common causes of anemia that affect DLCO include:
When we treat anemia, DLCO values often improve. This shows the lungs were working properly all along.
Pulmonary hypertension means high blood pressure in the lung arteries.
This condition affects blood flow through the lungs.
When blood vessels in the lungs are damaged or blocked, less blood flows past the air sacs.
This reduces how much oxygen can enter the bloodstream.
We see lower DLCO values in patients with:
The DLCO test helps us find these vascular problems early.
Some heart conditions can actually increase DLCO values.
Heart failure sometimes causes higher readings because extra blood vessels open up in the lungs.
DLCO measures how well gases move from your lungs into your blood.
Other tests like spirometry check airflow and lung volumes.
We use these tests together to get a complete picture of lung health.
DLCO and spirometry measure different parts of lung function.
Spirometry uses a spirometer to test how much air you can breathe in and out and how fast you can do it.
DLCO tests gas exchange between your lungs and blood.
It shows if oxygen can move properly from your air sacs into your bloodstream.
Spirometry helps us find breathing problems like asthma or COPD.
DLCO helps us spot lung diseases that affect gas exchange, like pulmonary fibrosis or emphysema.
A person might have normal spirometry but low DLCO, which could mean early lung disease.
This combination gives us more information than either test alone.
Spirometry measures several key values that work with DLCO results.
Forced vital capacity (FVC) is the total amount of air you can blow out after taking the deepest breath possible.
Forced expiratory volume in one second (FEV1) measures how much air you can blow out in the first second.
We use the FEV1/FVC ratio to spot airway blockages.
Total lung capacity (TLC) shows the maximum amount of air your lungs can hold.
Residual volume (RV) is the air left in your lungs after you breathe out completely.
These measurements help us understand different lung problems:
When we combine DLCO with other pulmonary function tests, we can identify specific disease patterns.
Normal spirometry with reduced DLCO often means early interstitial lung disease or pulmonary vascular problems.
Low DLCO with airway obstruction usually indicates emphysema rather than chronic bronchitis.
High or normal DLCO with asthma symptoms typically confirms asthma diagnosis.
We look at these patterns to make accurate diagnoses:
Test Results Likely Condition
Low DLCO + Normal spirometry Early lung disease, pulmonary hypertension
Low DLCO + Obstruction Emphysema
Normal DLCO + Obstruction Chronic bronchitis, asthma
Low DLCO + Low TLC Pulmonary fibrosis
DLCO testing requires careful attention to patient preparation and testing conditions to ensure accurate results.
Several factors can affect the test’s reliability, making proper protocols essential for meaningful interpretation.
Multiple conditions can alter DLCO results and affect their clinical value.
Hemoglobin levels play a major role since carbon monoxide binds to red blood cells.
Anemia decreases DLCO readings, while conditions causing blood in the airways can falsely increase values.
Smoking significantly impacts results.
Patients must avoid smoking for at least 4 hours before testing, though avoiding it on the test day is preferred.
Smoking affects carbon monoxide levels in blood and can lead to inaccurate measurements.
Exercise before testing can alter lung function temporarily.
We recommend patients avoid physical activity before their appointment.
Oxygen therapy must be stopped 15 minutes before testing.
Supplemental oxygen can interfere with gas exchange measurements and affect the accuracy of results.
Respiratory infections or acute illness can temporarily reduce DLCO values.
Testing should be postponed when patients have active respiratory symptoms.
Proper patient preparation ensures reliable test results.
Testing requires specific contraindications to be considered. Patients should not undergo DLCO testing within one month of a heart attack due to safety concerns.
Relative contraindications include chest pain, abdominal pain, facial pain, stress incontinence, and confusion or dementia. These conditions can prevent patients from following test instructions properly.
The test protocol is strict. Patients must inhale rapidly to full lung capacity within 4 seconds.
They should hold their breath for exactly 10 seconds, then exhale completely. The inspiratory volume should reach 90% or more of their best vital capacity measurement.
We typically perform at least two acceptable tests, with results within 2 mL/min/mm Hg of each other. More than five attempts per session can decrease DLCO values by up to 3.5%.
DLCO testing is a powerful diagnostic tool that helps uncover how efficiently your lungs transfer oxygen into your blood—often before symptoms even appear. Whether you’re managing a chronic condition or seeking clarity on unexplained shortness of breath, Gwinnett Pulmonary & Sleep offers precise testing and expert guidance every step of the way.
Call us or schedule your pulmonary function test today to take control of your lung health with the trusted experts in Gwinnett County.
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