Do you sometimes feel a little short of breath? Or do you often cough or wheeze? When you have symptoms like these, our doctors will ask you to do some tests to find out exactly how your lungs are working. One such important test is the DLCO. This test measures how well your lungs are absorbing oxygen into your blood. Let's talk about this simply, in a way that you can understand.
What does this DLCO test actually do? What is 'diffusion'?
Simply put, the DLCO (Diffusing capacity of the lungs for carbon monoxide) test measures how efficiently oxygen moves from your lungs into your blood. This is a type of pulmonary function test. It can give your doctor a clear idea of how well your lungs are working.
Now let's look at what this 'diffusion' is. Imagine, when you breathe, clean air (oxygen) goes through your nostrils, down your trachea, and into the tiny, grape-shaped air sacs (alveoli) in your lungs. There are millions of these air sacs, like tiny balloons. These air sacs are surrounded by a network of tiny blood vessels (capillaries). It is through these blood vessels that the oxygen that has come into the air sacs is absorbed into the blood. The blood then carries this oxygen throughout the body and allows our cells to produce energy.
This transfer of oxygen from the air sacs to the blood is what we call ``diffusion.'' Several factors affect the proper functioning of this diffusion:
- The surface area of your air sacs (alveoli) (i.e. the space available to absorb oxygen).
- How much blood is in the blood vessels (capillaries) around those air sacs.
- How much hemoglobin, a protein that carries oxygen, is in your blood.
- The thickness of the membrane between the air sacs (alveoli) and the blood vessels (capillaries). (This needs to be thin to allow oxygen to pass through well.)
- Whether there is excess fluid inside the air sacs (if there is fluid, it will interfere with the passage of oxygen).
Do you understand? It is very important for our lives that this process happens properly.
In what cases is this DLCO test performed?
There are several reasons why a doctor might ask you to have this DLCO test. Let's take a look at what they are:
- Find the cause of some of your symptoms: For example, if you have symptoms like shortness of breath, a persistent cough, or chest tightness, this test can help determine if the cause is a problem with your lungs absorbing oxygen.
- Assess lung damage: This is important to determine whether the lungs have been damaged, whether due to certain diseases or other causes, and if so, to what extent.
- Screening for some lung diseases: This test helps to detect some lung diseases at an early stage.
- Check your lungs before surgery or starting a strenuous exercise program: This test is done to see how well your lungs can withstand major surgery or before starting a new strenuous exercise program.
- Understand how another underlying condition may be affecting lung function: For example, if you have another condition, such as rheumatoid arthritis, this is important to find out if it is also affecting your lungs.
- Find out how effective an ongoing treatment is: If you are being treated for a lung disease, this test can see if the treatment has improved the lungs' ability to absorb oxygen.
- Monitor whether an existing medical condition is improving or worsening: This test also helps monitor the progress of a long-standing lung condition.
How is this DLCO test done? Can you explain a little bit?
This DLCO test uses a special gas mixture to measure how well oxygen (and carbon dioxide) is being exchanged between your lungs and your blood.
During the test, you will be given a mixture of two gases in addition to the nitrogen and oxygen gases that you normally breathe. These are:
- A very small amount of carbon monoxide: This is not harmful to you at all, so don't worry. Carbon monoxide gas is easily absorbed from the lungs into the blood.
- A very small amount of 'tracer gas': For example, a gas like methane. This tracer gas is not absorbed into the blood. This is what helps to measure exactly how much carbon monoxide has been absorbed into your blood.
When you breathe in this special mixture of gases, some or all of the carbon monoxide in the gas is absorbed into your blood. Then, when you breathe out into the machine, the machine measures how much carbon monoxide is left in the air you exhale. This calculates how much carbon monoxide has been absorbed into your blood. This measurement gives your doctor important information about how well your lungs are working.
How should we prepare before the test?
Before the DLCO test, your doctor or the lab technician will give you some instructions. They usually say things like this:
- You should stop smoking about four to six hours before the test.
- If you are using supplemental oxygen, you should stop using it about 10 minutes before the test (this only applies if it is safe for you to do so).
- Do not do strenuous exercise right before the test.
Following these instructions carefully is very important to obtain accurate test results.
What happens during the test? Is there anything to be afraid of?
The DLCO test is very simple and painless . It feels like a breathing exercise. Here's what happens:
1. The technician performing the test will place a small clip on your nose to prevent breathing out through that nostril.
2. Then you are asked to breathe into a mouthpiece connected to a machine . The special air mixture comes from this machine. Your breathing pattern and all the results are recorded by this machine.
3. First, you will be told to take slow, normal breaths .
4. Next, take a deep breath and exhale completely .
5. Then, take a deep breath through your mouth and hold it for about 10 seconds .
6. Finally, exhale completely .
After doing this once, the technician waits a few minutes and repeats the test once or twice more to get the most accurate reading. The entire test takes only a few minutes.
It's very simple, isn't it? There's nothing to worry about. If you feel anything uncomfortable, tell the technician right away.
Are there any risks to this test? Are there any side effects?
The risks of the DLCO test are very low. Some people may feel a little light-headed during the test. But this is normal. As mentioned earlier, the amount of carbon monoxide in the air you breathe is very small. It will not harm your body in any way. So don't worry about this.
How to understand the results of the DLCO test?
The results of a lung diffusion test are given as a percentage of what your DLCO value is expected to be (predicted value). Not everyone's expected DLCO value is the same. It depends on several factors, such as your age and gender. Your results may look like this:
- Normal DLCO: If it is between 75% and 140% of the expected value, it is normal.
- Mildly reduced DLCO: Between 60% and 75% of expected value or close to the lower limit of normal (LLN).
- Severely reduced DLCO: Less than 40% of expected value.
What does low DLCO value mean?
A low DLCO value simply means that your lungs are not efficiently taking oxygen from the air and delivering it to your blood. This could be due to a problem with your heart or lungs. For example, your heart may not be pumping blood properly, or your blood may not be absorbing enough oxygen.
What are the reasons for the decrease in DLCO value?
There can be many reasons why DLCO levels may decrease. Some of the main contributing factors are:
- Smoking: This is a major factor that contributes to a decrease in DLCO levels.
- Lung-related diseases:
- `Cystic fibrosis`
- `COPD (Chronic Obstructive Pulmonary Disease)` - Chronic Obstructive Pulmonary Disease
- Emphysema - abnormal swelling of the lung air sacs
- Sarcoidosis and other interstitial lung diseases
- Heart and blood related conditions:
- Pulmonary embolism (PE) - a blood clot in the lungs
- Pulmonary arterial hypertension - high blood pressure in the pulmonary arteries
- Congestive heart failure
- Anemia
- Diseases caused by weaknesses in the immune system (`Autoimmune disorders`):
- ``Mixed connective tissue disease''
- `Scleroderma`
- `Lupus (SLE)`
Conditions like these can reduce the lungs' ability to exchange oxygen.
Can DLCO levels increase? Why does that happen?
Yes, sometimes the DLCO value can be higher than expected. There are several reasons for this:
- Obesity
- Asthma
- Exercising before the test (that's why I said not to exercise before)
- Living at high altitudes
- Bleeding in your lungs
- Some heart conditions (`Cardiac shunt`, some cases of `Heart failure`)
- Polycythemia vera (an abnormal increase in blood cells)
In such cases, the DLCO value may also change.
What to do next if the results are abnormal?
If your DLCO test results are outside the normal range, meaning they are either too low or too high, your doctor will consider those results along with the results of your other lung function tests (for example, spirometry) and your symptoms to reach a conclusion.
Don't be afraid. Don't make big decisions based on the results of just one test.
The doctor may need more information. In such cases, he may order additional tests (e.g., chest X-ray, CT scan). All of this is done to better understand your condition and provide you with the best treatment possible.
Things we need to remember in summary (Take-Home Message)
Okay, so here's a summary of what we've talked about in this DLCO test to help you remember some of the most important points:
- The DLCO test is a painless, safe test that measures how well your lungs absorb oxygen into your blood.
- This helps your doctor find the cause of symptoms like shortness of breath and cough, diagnose lung diseases, monitor the success of treatments, and check the condition of your lungs before surgery .
- It is important to follow the doctor's instructions carefully before the test to obtain accurate results.
- If the test results are abnormal, don't panic and talk to your doctor to discuss what to do next.
If you have any questions about this test or your results, please ask your doctor. Then you will have a clear understanding. Stay healthy!
` Lung diffusion test, DLCO, oxygen exchange, lung function, respiratory disease, carbon monoxide, lung health
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