Pulmonary Function Test
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Learn what to expect when visiting the Emergency Department. Learn More
Overview
A Pulmonary Function Test (PFT) measures how well your lungs are working — how much air they can hold, how quickly you can move air in and out, and how well oxygen passes from the lungs into your blood. It is the essential test for asthma, COPD, and many other lung conditions. Especially in Delhi, where air quality affects so many people, PFT is one of the most useful and most under-used diagnostic tests we offer.
What is this test?
PFT is not a single test but a set of breathing tests. The most common is spirometry — you breathe into a mouthpiece while a machine measures how much and how fast you can move air. Other components include lung volume measurement (in a sealed chamber) and diffusion capacity (which measures how well oxygen crosses from your lungs into your blood). In some cases, the test is repeated after you inhale a bronchodilator (an asthma puffer) to see whether airway narrowing reverses. This is called a reversibility test.
When is this test recommended?
- Anyone with a chronic cough lasting more than 3 weeks
- Suspected asthma — wheeze, breathlessness, especially at night or with exercise
- Suspected COPD — typically smokers over 40 with persistent symptoms
- Long-term smokers being screened for lung disease
- Unexplained breathlessness or reduced exercise tolerance
- Before some major surgeries to assess fitness
- Monitoring a known lung condition over time
- Occupational lung disease assessment
Why your doctor may order it
- Diagnosing asthma and distinguishing it from other causes of breathlessness
- Diagnosing and grading COPD
- Tracking response to inhaler treatment
- Assessing fitness before lung surgery or transplant
- Investigating interstitial lung disease
- Long-term monitoring of chronic lung conditions
How long does it take?
Basic spirometry: 15 to 20 minutes. With reversibility testing (post-bronchodilator): 30 to 45 minutes. A full PFT panel (with lung volumes and diffusion): 45 to 60 minutes.
How to prepare
- Avoid smoking for at least 4 hours before the test (and ideally on the day).
- Avoid heavy meals and large drinks within 2 hours of the test — a full stomach can affect deep breathing.
- Avoid heavy exercise for 30 minutes before the test.
- Avoid alcohol for 24 hours before.
- Inhalers: ask your doctor which to stop and when. As a guide — short-acting inhalers (salbutamol) for 6 hours, long-acting (LABA/LAMA) for 12 to 24 hours. Do NOT stop any medication without checking first.
- Wear loose clothing that doesn't restrict chest movement.
- Bring your prescription, list of all inhalers and medicines, and any previous PFT reports.
What to expect during the test
You sit on a chair. A soft clip is placed on your nose to make sure all the air goes through your mouth. You wrap your lips tightly around a mouthpiece. The technician will coach you through the breaths — usually a slow, full breath in, then a hard, fast blast out, then a long steady continued exhale until your lungs are empty. Each manoeuvre lasts 6 to 10 seconds and is repeated several times to ensure reliable results.
If reversibility is being tested, you inhale a bronchodilator (usually salbutamol) and the spirometry is repeated 15 minutes later. The test takes effort. You may feel a little dizzy or breathless during the harder manoeuvres — this is normal and passes quickly.
After the test
- You can resume normal activities immediately.
- If a bronchodilator was given, you may feel mild jitteriness or a faster heart rate for 30 to 60 minutes — this is normal.
- Take your usual inhalers as normal from the next dose onwards.
- The report is typically available the same day.
- Your doctor will explain the result — including how your lung function compares with normal for your age, sex, and height.
Do's and Don'ts
- Follow the medication instructions carefully — wrong preparation often means the test has to be repeated.
- Eat lightly before the test, but don't skip it.
- Give your best effort — the test only works if you blow as hard and as long as you can.
- Tell the technician if you feel dizzy or unwell during the test.
- Bring all your inhalers with you in case the team needs to confirm what you take.
- Don't smoke before the test.
- Don't have a heavy meal within 2 hours.
- Don't stop your inhalers without medical advice — only the ones your doctor specifies.
- Don't be discouraged if the first attempt isn't perfect — several attempts are standard.
- Don't ignore a low score — many people with abnormal PFT have no obvious symptoms yet.
Understanding your results
PFT results are compared with predicted normal values for your age, sex, and height. The key numbers are FEV1 (how much air you can blow out in 1 second), FVC (total air you can blow out), and the FEV1/FVC ratio.
An obstructive pattern (asthma, COPD) shows reduced FEV1 with a low FEV1/FVC ratio. A restrictive pattern (lung scarring, chest wall problems) shows reduced FVC with a normal ratio. Reversibility — improvement after a bronchodilator — points strongly towards asthma. Your pulmonologist will interpret the full picture.
Frequently asked questions
No, but it is effortful. You will need to blow hard and long several times. Some people find this tiring; brief dizziness is normal and passes quickly.
Yes, usually from around age 6 or 7, when they can reliably follow the coaching. For younger children, other tests are used.
Some lung conditions are detected before symptoms become obvious — especially in long-term smokers or people with significant air pollution exposure. Early detection means earlier, more effective treatment.
Sometimes — that is the point. Stopping certain inhalers before the test helps the team see how your lungs behave without medication. Don't stop anything without specific instructions.
It depends. People with stable asthma or COPD may have one every 1 to 2 years. After major treatment changes, sooner. Your pulmonologist will recommend the right interval.