Have you ever wondered what kind of testing is involved in diagnosing, managing, or treating PF? Whether you have a PF diagnosis or suspect you might be tested for it, there are a lot of terms that can seem confusing or overwhelming. To learn about getting diagnosed with PF, visit Part 1 of our FAQs here. To learn about managing PF, visit Part 2 of our FAQs here. To better understand what pulmonary function tests (PFTs) are – including how they’re done, what to expect, and what the results can show – keep reading below…
Why are pulmonary function tests done?
Pulmonary function tests (PFTs) are used to measure how well your lungs are working. A common office test to measure lung function is spirometry. This test measures the amount of air your lungs can hold (lung capacity) and how forcefully you can empty air from your lungs (lung function). PFTs are used to diagnose chronic lung conditions such as pulmonary fibrosis, asthma or COPD and other conditions that affect breathing. Spirometry results can help determine which type of lung disease you have and its severity. PFTs are also used periodically to monitor disease progression and to determine if your treatment is helping you breathe better.
What can you expect during a spirometry test?
A spirometry test requires you to take a deep breath in and forcefully breathe out as hard and fast as you can into a tube which is connected to a machine called a spirometer. A clip is placed on your nose to prevent air from coming out of your nostrils. You will receive specific instructions throughout the test from a nurse or technician to ensure you do the test correctly and get accurate results. It is generally repeated 3 times to make sure the results are consistent since the numbers are dependent on the effort you put in during the testing. The testing process can take up to 15 minutes. Here is a video link from the National Heart Lung and Blood Institute (NHLBI) on taking a spirometry test: https://www.youtube.com/watch?v=Zs8Fs5HaJHs
What do normal predicted values in a pulmonary function test mean?
Your PFT results are generally presented and discussed as a percentage of predicted. This is because there are many variables that affect lung size and thus, PFT numbers. Four variables that go into the equation that calculates what a normal value of a PFT are height, age, gender and race. This comes up with a customized normal value for each individual. The normal or predicted values are based upon research on hundreds of thousands of people with normal lung function.
What values do you see on a pulmonary function test report?
There are many abbreviations and numbers on a PFT report. Some of the important ones are:
- TLC or Total Lung Capacity: which is the maximum amount of air your lungs can hold after taking in a deep breath. Measuring TLC helps in diagnosing and monitoring your lung disease. Changes in TLC over time can indicate disease progression, effectiveness of your treatment or the impact of interventions such as pulmonary rehabilitation.
- VC or Vital Capacity: records the maximum amount of air you can breathe in and out of your lungs. The normal range of VC for an adult is 3 to 5 liters and your value will be compared to a standardized or normal value as described above. Restrictive lung diseases like PF make it harder for you to fully fill your lungs with air due to increased lung stiffness and can cause your VC to decrease.
- Tidal volume: is a measure of the amount of air you breathe in and out when you are breathing normally. It measures around 500 ml in an average healthy male and around 400 ml in a healthy female. In PF, the tidal volume decreases, and the patient can develop a breathing pattern of rapid shallow breaths to minimize the work of breathing.
- FVC or Forced Vital Capacity: is a measure of the maximum volume of air that can be forcefully exhaled from your lungs after maximum inhalation i.e., after taking the deepest breath possible. FVC measures the effect that your lung disease has on your ability to inhale and exhale. In restrictive lung diseases such as PF and sarcoidosis, there is a problem inhaling air to fill your lungs so this number is reduced. FVC values 80 – 120% of the predicted value are considered to be normal.
- FEV1 or Forced Expiratory Volume1: is the volume of air that can be forcefully exhaled in the 1st second during the FVC exercise. It is used to determine the severity of disease. FEV values 80 – 120% of the predicted value are considered to be normal; 70-79% = mildly abnormal; 60 to 69% = moderately abnormal; 50-59% = moderately to severely abnormal; 35-49% = severely abnormal; and less than 35% = extremely abnormal.
- FEV1/FVC ratio: In pulmonary fibrosis, the FEV1 and FVC may both be equally reduced due to fibrosis so the ratio is generally normal or even increased due to a greater decrease in FVC as compared to FEV1. In people with PF, the ratio is greater than 70%.
- FEF25-75 or the Forced Expiratory Flow 25-75: measures airflow during the middle half of the test and can detect impairment in small airways.
- DLCO or Diffusing Capacity of the lung for Carbon monoxide: which is a type of PFT that measures the ability of your lungs to transfer gas from the inhaled air into the blood stream. It uses a gas containing micro amounts of carbon monoxide to measure how much oxygen moves from your lungs into your blood when you inhale. One of the factors that determine how well oxygen transfers from your lungs to your blood is the thickness of the space (which is called the interstitium) between your alveoli and capillaries. In PF, there is thickening and stiffness of the interstitial space and thus the DLCO value decreases. A low DLCO means that your lungs are not getting oxygen from the air to your blood efficiently. DLCO values of 75-140% of the predicted value are considered normal; greater than 60-75% = mildly reduced; 40–60% = moderately reduced and less than 40% = severely reduced.
Can a pulmonary function test tell you what stage of pulmonary fibrosis you are in?
There is no specific staging system for PF and the rate of progression can be very different in people and is somewhat unpredictable. Based on PFT results, your doctor may stage your PF as mild, severe or advanced. PFTs are generally done every 6 months to see if your disease is getting worse and to check your response to treatment. Changes in lung function over time is an important indicator of your lung health.
To conclude, your doctor will use these results along with additional tests including the 6-minute walk test, imaging, blood work, physical examination etc. to diagnose your condition, to see how well your treatment is working, and to assess progression.
It’s February – did you know Rare Disease Day is coming up at the end of this month?!
While diseases like PF are technically rare, they impact countless individuals in our lives. This is a time for us all to come together, increase awareness, advocate, and educate. Learn more about Rare Disease Day here, view the agenda here, and register to virtually attend here. Until then, let’s focus on PF by attending support group meetups and engaging in our community forum. Your questions could make it onto our next FAQs page! To submit additional questions for consideration, contact firstname.lastname@example.org
Stay In Touch
PF NOW! hosts virtual support groups on Teams multiple times each month. Not only will you strengthen your network of connections but you’ll learn firsthand how those with PF best look after themselves. PF NOW! also has a Facebook group whose active community shares their PF journey and their tips with others. New to online support groups? Download our free step-by-step guide for online advocacy here.
Never disregard professional medical advice or delay in seeking it because of any information received from us.