During diagnosis of pulmonary fibrosis or interstitial lung disease, your doctor will administer a pulmonary function test (PFT). A pulmonary function test, also called a lung function test, is a set of tests that measure how well your lungs are working.
Most common test is inhaling and exhaling
The most common type of lung function test is spirometry, which measures how much air you can breathe in and out. To perform the test, you inhale deeply and forcefully exhale into a tube that is connected to a device called a spirometer.
The important measures for pulmonary fibrosis are FVC and FEV
The scarring that comes with pulmonary fibrosis makes your lungs stiff and can restrict the expansion of your lungs when you inhale. If your lungs do not expand fully, they may hold less air than unscarred lungs.
The most important measures on the tests for pulmonary fibrosis patients are:
- Forced vital capacity (FVC). A measure of the total amount of air exhaled during the FEV test. Forced expiratory volume is an important measurement of lung function.
- Forced expiratory volume (FEV). A measure of how much air a person can exhale in one second during a forced breath. The amount of air exhaled can be measured during the first, second, and third seconds of a breath during a FEV test; respectively called FEV1, FEV2, and FEV3. Decreases in the FEV1 value may mean lung disease is getting worse.
- FEV1/FVC – The ratio is the ratio of these two numbers. The normal value for this ratio is above 0.75-85, though this is age dependent.
Results are shown as liters and percent
Forced vital capacity and forced expiratory volume results are reported:
- As a number in liters (L)
- As a percentage of the predicted reference of healthy lungs
- As a graph showing the changing aspect of your exhalation
The pulmonary function test results compare your FVC and FEV to the results that are expected from a person of the same sex, age, and height with normal lung function. The normal measures are called the reference (REF) or predicted (PRE) value.
A normal result is 80% or higher
The normal FVC range for an adult is between 3.0 and 5.0 L. Note that different clinics or hospitals may use slightly different standards. If your FVC and the FEV1 are within 80% of the reference value, the results are considered normal. The normal value for the FEV1/FVC ratio is 70% (and 65% in persons older than age 65).
PF patients usually have a lower than normal FVC and FEV
Patients with pulmonary fibrosis typically have FVC and FEV values that are lower than the normal value. This means that the lung is restricted from filling to normal capacity.
Meanwhile, FEV1/FVC ratio is often in the normal range or higher than normal for someone with pulmonary fibrosis. This happens when you inhale a smaller than normal amount of air and can exhale all of it or even more.
Abnormal results range from mild to severe
Your doctor should give you the results of your pulmonary function test and explain the results to you. The closer your FVC and FEV results are to the reference or predicted number, the healthier your lungs are. Your lungs are considered normal when your percentage of the predicted value is 80% or better. In the sample shown, the patient’s FVC and FEV are 49% and 56% respectively, which shows severe restriction of lung function. While pulmonologists do not refer to stages of pulmonary fibrosis, some will use the table below to describe the restriction as normal, mild, moderate, or severe.
For both FVC and FEV, the following ranges can describe how severe the restriction is:
- 80% and higher is normal
- 70 – 79% is mild
- 60 – 69% is moderate
- Less than 60% is severe
Your FVC/FEV ratio may be higher than normal, as is shown in the sample report above. This higher result is expected with pulmonary fibrosis and indicates a restrictive disease, rather than obstructive diseases (such as COPD).
You will take this test during often during the course of your journey. Your pulmonologist may have you repeat this test every 3 or every 6 months. Your pulmonologist uses the results to monitor any changes to your lungs, the effectiveness of therapy, the progression of your disease, and to decide whether additional tests are needed.
You can also track your FVC and FEV values over time. This can determine whether your pulmonary condition is progressing or if your lung function is stable under treatment.
What are all those other numbers?
In addition, the test can also measure other details. For your information, these are:
- Tidal volume (VT). This is the amount of air inhaled or exhaled during normal breathing.
- Minute volume (MV). This is the total amount of air exhaled per minute.
- Vital capacity (VC). This is the total volume of air that can be exhaled after inhaling as much as you can.
- Functional residual capacity (FRC). This is the amount of air left in lungs after exhaling normally.
- Residual volume. This is the amount of air left in the lungs after exhaling as much as you can.
- Total lung capacity. This is the total volume of the lungs when filled with as much air as possible.
- Forced expiratory flow (FEF). This is the average rate of flow during the middle half of the FVC test.
- Peak expiratory flow rate (PEFR). This is the fastest rate that you can force air out of your lungs
If your lung function test results are not normal, it may indicate that you have a lung disease. Ask your healthcare provider to explain the results to you and ask them what the numbers mean for you. Ask your healthcare provider about pulmonary rehabilitation, which can strengthen your overall health and help you cope with shortness of breath and other symptoms of lung disease. Your pulmonologist may follow up your lung function test with other tests, such as arterial blood gas tests or a high-resolution CT Scan to look for specific patterns of scarring in your lungs. Remember, there are treatments and therapies for pulmonary fibrosis. While some patients have scarring that progresses rapidly, other have scarring that progresses slowly. The lung function test is just one of the tests that doctors use the assess your health.