Jul 24, 2026 How to Prepare for a Pulmonary Function Test: What to Know
If your healthcare provider has scheduled a pulmonary function test (PFT), you may be wondering how to prepare, what the test involves, and what not to do before a pulmonary function test. These are some of the most common questions patients ask before their appointment. Understanding what to expect can help you feel more confident and help ensure your test results are as accurate as possible.
Pulmonary function tests are non-invasive breathing tests that help evaluate how well your lungs are working. They are commonly used to diagnose and monitor conditions such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and other respiratory conditions.
Proper PFT preparation is important because certain medications, foods, drinks, and activities can temporarily affect your breathing or lung function. Following your healthcare provider’s instructions helps ensure the results reflect your typical lung function rather than temporary changes that could influence the measurements.
Whether you’re having a simple spirometry test or a complete pulmonary function evaluation that includes lung volumes and diffusing capacity (DLCO), understanding the process can help you arrive prepared and ready for your appointment.
What a Pulmonary Function Test Measures
A pulmonary function test is actually a group of breathing tests that evaluate different aspects of lung function. Your healthcare provider orders the tests based on the questions they’re trying to answer about your breathing.
Some patients only need spirometry, while others benefit from a complete pulmonary function test (PFT) that also measures lung volumes and diffusing capacity (DLCO). Together, these tests provide a more comprehensive picture of how your lungs are functioning.
Spirometry
Spirometry measures:
- How much air you can breathe in and out
- How quickly you can exhale
- Whether airflow is reduced or obstructed
Spirometry is commonly used to help diagnose and monitor asthma, COPD, and other conditions that affect the airways.
Lung Volume Testing
Lung volume testing measures how much air your lungs can hold and how much air remains after you exhale.
These measurements help providers determine whether reduced breathing capacity is caused by restrictive lung disease, air trapping, or another condition that spirometry alone cannot fully explain.
Diffusing Capacity (DLCO)
A DLCO test measures how efficiently oxygen moves from your lungs into your bloodstream.
This test may help evaluate conditions such as:
Pulmonary fibrosis
Emphysema
Pulmonary hypertension
Other diseases that affect gas exchange
By combining spirometry, lung volumes, and DLCO, healthcare providers gain a more complete understanding of your respiratory health and can make more informed treatment decisions.
What Not to Do Before Your Test
One of the most common questions patients ask is, “What not to do before a pulmonary function test?”
While your healthcare provider will give you instructions specific to your situation, these general guidelines are commonly recommended.
Don’t Smoke
If possible, avoid smoking before your appointment if instructed by your provider.
Smoking can temporarily narrow your airways and affect how well your lungs perform during testing. Avoiding tobacco beforehand helps ensure your results reflect your normal lung function.
Don’t Exercise Strenuously
Heavy exercise shortly before your appointment can temporarily change your breathing pattern and heart rate.
For the most accurate results, avoid vigorous exercise for several hours before your test unless your provider gives you different instructions.
Don’t Wear Tight Clothing
Tight clothing around your chest or abdomen can make it more difficult to take deep breaths during testing.
Loose, comfortable clothing allows you to breathe naturally and perform the breathing maneuvers more easily.
Don’t Eat a Heavy Meal Right Before Your Appointment
A very full stomach can make it uncomfortable to take deep breaths or exhale forcefully.
A light meal is usually a better choice before pulmonary function testing unless your provider advises otherwise.
Don’t Ignore Your Provider’s Instructions
Preparation instructions may vary depending on why your provider ordered the test.
If your healthcare team gives you instructions that differ from general recommendations, always follow their guidance.
Medications to Pause and When to Ask
One of the most important parts of how to prepare for a pulmonary function test is understanding whether you should take your usual inhalers or breathing medications.
The answer depends on the purpose of your test.
Sometimes your provider wants to measure your lung function before using a bronchodilator. Other times they want to see how much your breathing improves after taking medication.
Because of this, some patients may be asked to temporarily hold certain inhalers before testing.
These may include:
- Short-acting rescue inhalers
- Long-acting bronchodilators
- Combination inhalers
However, never stop or delay any prescribed medication unless your healthcare provider specifically instructs you to do so.
If you’re unsure:
- Ask when scheduling your appointment.
- Bring an updated list of your medications.
- Contact your healthcare provider before the day of your test if you have questions.
If you use supplemental oxygen, ask whether you should bring your equipment or whether oxygen will be available at the testing facility.
Food, Caffeine, and Drinks Before Testing
Many patients wonder whether they should eat or drink before a pulmonary function test.
In most cases, yes. However, a few simple precautions can help ensure accurate results.
Eat Lightly
A heavy meal can make it more difficult to take the deep breaths required during testing.
Eating a light meal several hours before your appointment is often recommended.
Ask About Caffeine
Some providers recommend avoiding coffee, tea, energy drinks, or other caffeinated beverages before testing because caffeine may affect certain medications or breathing responses.
If you were not given instructions about caffeine, it’s a good idea to ask before your appointment.
Stay Hydrated
Drinking water is generally encouraged unless your provider advises otherwise.
Staying hydrated can help keep your mouth and throat comfortable during repeated breathing maneuvers.
Avoid Alcohol
Alcohol may affect your breathing effort, coordination, or medications.
Avoiding alcohol before pulmonary function testing is generally recommended.
What to Wear and Bring
Preparing for your appointment doesn’t require much, but wearing the right clothing and bringing a few essentials can make the visit easier.
Wear Comfortable Clothing
Choose clothing that allows you to take deep breaths comfortably.
Good choices include:
- T-shirts
- Athletic wear
- Loose-fitting tops
- Comfortable pants
Avoid restrictive clothing such as:
- Tight belts
- Corsets
- Tight shapewear
- Tight dresses or jackets
Bring What You’ll Need
Bring:
- Identification
- Insurance information if required
- A list of your medications
- Your inhalers, unless instructed otherwise
- Any paperwork requested by your provider
If you wear hearing aids or glasses, continue wearing them so you can clearly hear and follow the technologist’s instructions.
How Long the Test Takes
Another common question is, “How long does a pulmonary function test take?”
The answer depends on which tests your provider has ordered.
Typical appointment times include:
- Spirometry: approximately 15 to 30 minutes
- Complete pulmonary function testing: approximately 45 to 90 minutes
- Testing before and after bronchodilator medication: additional time may be needed to allow the medication to take effect
Some breathing maneuvers may be repeated several times to ensure the results are accurate and reproducible. Your technologist will coach you through each step and allow you to rest between attempts if needed.
What the Test Feels Like
If you’ve never had a pulmonary function test before, it’s normal to feel a little nervous.
The good news is that pulmonary function tests are non-invasive and generally well tolerated.
During the test, you’ll be asked to:
- Breathe normally
- Take the deepest breath you can
- Blow out as hard and as fast as possible
- Hold your breath briefly during certain measurements
- Repeat some breathing maneuvers several times
Some patients feel slightly winded or lightheaded after blowing out forcefully, but these sensations usually pass within a few seconds. Your technologist will monitor you throughout the test and allow you to rest whenever needed.
A More Comfortable Way to Measure Lung Volumes
Many people have heard of the traditional body plethysmograph, often called a “body box.” This test requires patients to sit inside a clear enclosed chamber while lung volume measurements are taken.
While body boxes have been used successfully for many years, they are not the only option.
Today, some clinics use cabinless lung volume technology, which measures lung volumes without requiring patients to sit inside an enclosed chamber.
For many patients, especially those who experience claustrophobia, anxiety in confined spaces, or mobility limitations, this more open testing environment can make the experience feel more comfortable.
Technologies such as the PulmOne MiniBox+ combine cabinless lung volume measurement with spirometry and DLCO testing in one compact system. Although the breathing instructions are similar, many patients appreciate the open design and streamlined testing experience.
No matter which system your clinic uses, the goal is the same: to collect accurate, reliable information that helps your healthcare provider better understand your lung health.
What Your Results Can Show
Your pulmonary function test provides valuable information about how well your lungs are working, but the results are only one piece of the puzzle.
Your healthcare provider will review your measurements alongside your symptoms, medical history, physical examination, and, if needed, imaging studies or other diagnostic tests.
Pulmonary function testing can help evaluate conditions such as:
- Asthma
- COPD
- Pulmonary fibrosis
- Restrictive lung disease
- Emphysema
- Pulmonary hypertension
- Airway obstruction
- Reduced lung capacity
Your report may include measurements such as:
- FEV₁
- FVC
- FEV₁/FVC ratio
- Total Lung Capacity (TLC)
- Residual Volume (RV)
- Diffusing Capacity (DLCO)
Your provider will explain what these numbers mean and how they relate to your individual health.
Frequently Asked Questions
Can I drive myself home afterward?
Yes. Pulmonary function tests do not require sedation, and most people can return to their normal daily activities immediately after testing unless their provider advises otherwise.
What if I have a cough on the day of my appointment?
A mild cough may not prevent testing, but a severe cough, fever, or symptoms of a contagious illness could affect your results or require your appointment to be rescheduled. Contact your testing center if you’re unsure.
Should I cancel if I’m feeling short of breath?
Not necessarily. Many pulmonary function tests are ordered because patients are experiencing breathing symptoms.
However, if you have sudden severe shortness of breath, chest pain, or difficulty breathing that feels like an emergency, seek immediate medical care and contact your healthcare provider.
Will I receive my results immediately?
Some clinics discuss results during the same visit, while others send them to your referring provider for interpretation. Ask your testing center what to expect.
Preparing for the Best Possible Results
Following your provider’s instructions is the best way to ensure your pulmonary function test accurately reflects your lung health. Knowing what not to do before a pulmonary function test, such as smoking, strenuous exercise, eating a heavy meal, or changing medications without guidance, helps reduce temporary factors that could affect your results.
Understanding what the test measures and what the experience is like can also help you feel more comfortable before your appointment. Whether you’re having spirometry alone or a complete pulmonary function test with lung volumes and DLCO, these measurements provide important information that helps your healthcare provider evaluate your breathing and guide your care.
For clinics, patient comfort is also an important part of the testing experience. In addition to delivering comprehensive pulmonary function testing, newer cabinless technologies such as the PulmOne MiniBox+ offer an alternative to traditional body-box lung volume testing. For many patients, the open design can make testing feel less intimidating while still providing the accurate, reliable measurements clinicians depend on.
With the right preparation and a clear understanding of what to expect, you can arrive at your appointment with confidence and help ensure the most accurate assessment of your lung health.