PFT (Pulmonary Function Test): Preparation, Procedure and How to Read Your Results

A pulmonary function test (PFT) measures how much air your lungs can hold and how fast you can blow it out. The core test is spirometry: you take a full breath and blow out as hard and as fast as you can into a mouthpiece. The main numbers are FVC (total air blown out), FEV1 (air blown out in the first second) and their ratio. A ratio below about 0.70 points to obstruction, as in asthma or COPD. A low FVC with a normal ratio suggests a restrictive problem, where the lungs cannot expand fully.

This guide explains how to prepare, what happens on the day, how to read each line of a report with worked examples, and what the common patterns look like.

Why doctors order a PFT

• Long-standing cough, wheeze or breathlessness
• To diagnose or monitor asthma and COPD
• To check lung function before surgery or when a condition is suspected
• To follow lung diseases such as interstitial lung disease or after tuberculosis
• To assess the effect of treatment, such as inhalers
• For occupational screening in dust-exposed workers
• To look at the impact of smoking, pollution or chest conditions
• To evaluate breathlessness that remains unexplained after a chest X-ray

The tests that make up a PFT

Spirometry

The main and most widely used test. It measures volume and flow.

Bronchodilator reversibility

Spirometry is repeated 15 to 20 minutes after you inhale a bronchodilator (such as salbutamol). It shows whether blocked airways open up, which is typical of asthma.

Lung volumes (body plethysmography or gas dilution)

Measures the total amount of air in the lungs, including air that can't be blown out (residual volume). It confirms restriction.

Diffusion capacity (DLCO)

Measures how well oxygen moves from air into blood. Low in emphysema, interstitial lung disease, pulmonary vascular disease and anaemia.

Other tests

A six-minute walk test, peak flow monitoring and oxygen measurements may be added.

How to prepare

• Tell the lab about your medicines. You may be asked to hold inhalers for a few hours (short-acting bronchodilators about 4 to 6 hours, long-acting for 12 to 24 hours or more). Don't stop anything without being told by your doctor or the lab.
• Don't smoke for at least 24 hours, and avoid alcohol for four hours before the test.
• Avoid a heavy meal for about two hours beforehand.
• Avoid vigorous exercise for at least 30 minutes before.
• Wear loose, comfortable clothing.
• Leave out heavy perfume or strong scents, which can trigger a cough.
• Skip caffeine for a few hours if the lab advises, since it can mildly affect airways.
• Postpone the test if you've had a recent chest infection (many labs wait 4 to 6 weeks), recent eye, chest or abdominal surgery, a heart attack in the last month, or an unexplained coughing up of blood. The lab will ask about this.
• Bring previous reports, inhalers and a list of medicines.

What happens during the test

1. You sit upright, and a nose clip is placed.
2. You breathe normally through a mouthpiece, then breathe in as deeply as you can.
3. You blow out forcefully and completely, as hard and as long as you can (at least six seconds, ideally until your lungs feel empty).
4. A technician coaches you, and you repeat the manoeuvre at least three times to ensure consistency.
5. If asked, you inhale a bronchodilator and the test is repeated after 15 to 20 minutes.

The whole test takes about 20 to 45 minutes. It isn't painful. You may feel light-headed or cough, and you should tell the technician if you feel dizzy.

Good effort matters. A weak or incomplete effort makes the numbers look worse than your real lung function.

The main numbers

| Measure | What it is | |---|---| | FVC (forced vital capacity) | Total air you can forcefully blow out after a full breath | | FEV1 | Air blown out in the first second | | FEV1/FVC ratio | FEV1 divided by FVC, the main marker of obstruction | | PEF (peak expiratory flow) | The fastest flow rate you reach | | FEF 25 to 75 | Flow in the middle of the breath; reflects smaller airways, but less reliable |

Results are compared with "predicted" values based on your age, sex, height and ethnicity. Because Indians generally have somewhat lower lung volumes than Western reference populations, reports using European reference equations may overcall abnormality. Labs should use appropriate reference equations. The report shows each value as a percentage of predicted.

Reading the pattern

Normal

• FEV1/FVC ratio at or above about 0.70 (or above the lower limit of normal)
• FVC and FEV1 at 80 percent of predicted or higher

Obstructive pattern (asthma, COPD, bronchiectasis)

• FEV1/FVC ratio below about 0.70
• FEV1 reduced, FVC normal or mildly reduced

Example. FEV1 = 2.1 litres, FVC = 3.5 litres. Ratio = 2.1 ÷ 3.5 = 0.60. That's obstructive. If the predicted FEV1 for this person is 3.0 litres, FEV1 is 2.1 ÷ 3.0 = 70 percent of predicted.

Restrictive pattern (interstitial lung disease, scoliosis, obesity, chest wall or muscle disease, after surgery)

• FEV1/FVC ratio normal or high (above 0.70)
• FVC reduced (below 80 percent of predicted)
• Confirmed by low total lung capacity

Example. FEV1 = 1.8 litres, FVC = 2.2 litres. Ratio = 1.8 ÷ 2.2 = 0.82. The ratio is normal but the FVC is low, which suggests restriction. The doctor will confirm with lung volumes.

Mixed pattern

A low ratio and a low FVC, with total lung capacity reduced.

Normal example

FEV1 = 3.0 litres, FVC = 3.8 litres. Ratio = 3.0 ÷ 3.8 = 0.79. If both are above 80 percent of predicted, the test is normal.

Grading severity of obstruction (as used for COPD)

The GOLD guideline classifies airflow limitation by post-bronchodilator FEV1 as a percentage of predicted, in people whose ratio is below 0.70:

| Grade | FEV1 (percent of predicted) | |---|---| | GOLD 1, mild | 80 or above | | GOLD 2, moderate | 50 to 79 | | GOLD 3, severe | 30 to 49 | | GOLD 4, very severe | Below 30 |

Doctors combine this with symptoms and the number of flare-ups to decide treatment.

Asthma or COPD? What the report suggests

| Feature | Asthma | COPD | |---|---|---| | Typical age at onset | Often childhood or young adult, can be any age | Usually over 40 with a smoking or smoke exposure history | | Airway obstruction | Variable, may be normal between attacks | Persistent | | Bronchodilator response | Often significant improvement | Little or no full reversal | | Symptoms | Wheeze, cough, night or early morning symptoms, triggers (dust, cold air, allergens) | Chronic cough, sputum, breathlessness on exertion |

A commonly used sign of reversibility: FEV1 rises by at least 12 percent and at least 200 mL after a bronchodilator. This supports asthma but doesn't exclude COPD, since the conditions can overlap.

Normal spirometry doesn't rule out asthma, because airways may be normal between episodes. A doctor may recommend peak flow diary or a challenge test.

DLCO

| DLCO | What it suggests | |---|---| | Low with obstruction | Emphysema | | Low with restriction | Interstitial lung disease | | Low with normal spirometry | Early lung disease, pulmonary vascular disease, anaemia | | High | Asthma, polycythaemia, bleeding in the lungs, obesity in some cases |

Why the result may not reflect your lungs

• Poor effort or technique
• Cough during the test
• Recent infection
• Wrong reference values for your ethnicity
• Incorrect height (spinal curvature)
• Not stopping inhalers as advised
• Pain or recent surgery

If a result doesn't match your symptoms, the test may be repeated.

What happens after the test

Your doctor interprets the report together with your symptoms, examination, chest X-ray or CT, and blood tests. Treatment may include inhalers, quitting smoking, vaccinations, pulmonary rehabilitation, treatment of the cause, oxygen in advanced disease, and in some cases referral for a specialist or sleep study.

Protecting your lungs

• Don't smoke. Stopping smoking is the single most effective step in COPD.
• Avoid indoor smoke from chulhas and biomass fuels, and use proper ventilation.
• On high-pollution days, limit outdoor exercise and consider a well-fitted N95-type mask outdoors.
• Take vaccines for influenza and pneumonia if advised.
• Use inhalers correctly and regularly as prescribed.
• Stay active; breathing exercises and pulmonary rehabilitation help.

Frequently asked questions

What is a PFT test?

A set of breathing tests, centred on spirometry, that measure lung volume and airflow to diagnose and monitor lung disease.

How do I prepare for a PFT?

Avoid smoking for 24 hours, skip heavy meals and exercise beforehand, wear loose clothes, and follow instructions about inhalers.

Is the PFT test painful?

No, but it needs strong effort. Some people feel dizzy or cough.

What is a normal FEV1/FVC ratio?

About 0.70 or higher in adults. In older adults, a ratio slightly below 0.70 can be normal for age.

What does a low FVC mean?

It suggests restriction, such as lung scarring or chest wall problems, but needs confirmation with lung volumes.

How long does a PFT take?

About 20 to 45 minutes, and longer if full lung volumes and DLCO are done.

Can I take my inhaler before the test?

Ask the lab. Often you will be asked to hold certain inhalers beforehand.

When to see a doctor

See a doctor if you have a cough lasting more than three weeks, wheeze, breathlessness on mild exertion, chest tightness, or coughing up blood. Seek urgent care for severe breathlessness, blue lips, difficulty speaking or chest pain.

Care at Prakash Hospital Noida

Whether you live in Sector 18, Sector 62, Greater Noida West, or anywhere nearby, Prakash Hospital Noida is a trusted name for pulmonology and respiratory care in Noida. Our specialists perform lung function tests, explain the results and design treatment around them.

To book a consultation, call the number.

Sources: American Thoracic Society and European Respiratory Society spirometry standardisation statements; GOLD report on COPD. Reference values vary by population; use appropriate local equations.

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