Introduction

Pulmonary function tests (PFTs), also known as lung function tests, are a group of noninvasive breathing tests that measure how well your lungs are working. These tests evaluate three key aspects of respiratory function: how much air your lungs can hold, how quickly you can move air in and out, and how efficiently your lungs transfer oxygen into your bloodstream. While PFTs are particularly effective at detecting the general type and severity of lung disorders, they can also help diagnose specific conditions such as asthma and chronic obstructive pulmonary disease (COPD).

Why Are Pulmonary Function Tests Needed?

Your doctor may recommend pulmonary function testing if you experience symptoms such as shortness of breath, persistent coughing, wheezing, or abnormal breathing sounds. These tests are also commonly used to:

• Diagnose lung diseases including asthma, COPD, bronchitis, and emphysema

• Monitor the progression of chronic lung conditions and evaluate treatment effectiveness

• Assess lung function before surgery

• Screen individuals with risk factors such as smoking history or occupational chemical exposures

• Evaluate disability and disease severity

The Basic Test: Spirometry

Spirometry is the most widely used and accessible pulmonary function test. It measures the volume and speed of air you can inhale and exhale. During the test, you sit upright with a soft clip on your nose to prevent air from escaping through it. You then take a deep breath, seal your lips tightly around a mouthpiece connected to a device called a spirometer, and exhale as quickly and forcefully as possible. This maneuver is typically repeated at least three times to ensure reliable results.

The most important measurements obtained from spirometry include:

• Forced Vital Capacity (FVC) – the total volume of air you can exhale during a forceful breath

• Forced Expiratory Volume in one second (FEV₁) – the amount of air you can exhale in the first second of a forced breath

• FEV₁/FVC Ratio – the proportion of total air exhaled in the first second, which helps identify whether airflow is obstructed or restricted

In healthy adults, the FEV₁/FVC ratio is typically around 75–80%. A lower ratio may indicate obstructive lung diseases such as asthma or COPD, while a reduced FVC with a normal ratio may suggest restrictive lung conditions.

Additional Pulmonary Function Tests

Beyond spirometry, a comprehensive pulmonary function evaluation may include several other tests:

• Lung Volume Measurement (Body Plethysmography) – This test measures the total amount of air your lungs can hold, including the air that remains after you exhale. You sit in a small, enclosed clear-walled booth and breathe through a mouthpiece while pressure changes are recorded.

• Diffusing Capacity Test (DLCO) – This measures how well gases, particularly oxygen, move from your lungs' air sacs (alveoli) into your bloodstream. You inhale a harmless tracer gas, hold your breath for a few seconds, and then exhale. The test reflects the lungs' primary function—delivering oxygen to the body.

• Bronchodilator Reversibility Test – After initial spirometry, you may be given an inhaled medication that opens your airways. The test is then repeated to see if your lung function improves, helping determine whether your condition is reversible.

• Peak Expiratory Flow Rate – This measures how fast you can exhale and is often used to monitor asthma.

• Fractional Exhaled Nitric Oxide (FeNO) – This test measures nitric oxide levels in your breath, which can indicate airway inflammation

How to Prepare for the Test

Proper preparation helps ensure accurate results. General guidelines include:

• Avoid smoking for 6 to 24 hours before the test

• Refrain from drinking alcohol for at least 4 to 24 hours beforehand

• Avoid heavy meals for 2 to 4 hours prior to testing

• Do not engage in strenuous exercise on the day of the test

• Wear loose, comfortable clothing that does not restrict your breathing

• Consult your doctor about whether to pause certain medications, particularly inhalers

What to Expect During the Test

Most pulmonary function tests are painless and carry minimal risk. Spirometry typically takes 15 to 30 minutes, while a full battery of tests may take 30 to 90 minutes. You may feel slightly dizzy, lightheaded, or tired after forceful exhalation, but these effects are usually temporary.

Understanding Your Results

Your test results are compared against predicted values based on your age, height, sex, and ethnicity. Results are generally considered abnormal if they fall below 80% of the predicted value. Your doctor will interpret the patterns to determine whether you have:

• Obstructive impairment – difficulty exhaling air quickly (common in asthma and COPD)

• Restrictive impairment – reduced lung volume (common in pulmonary fibrosis and chest wall abnormalities)

• Mixed impairment – a combination of both patterns

Safety and Contraindications

Spirometry is safe for most people. However, the test may not be suitable if you have recently experienced a heart attack, have unstable angina, uncontrolled high blood pressure, or have undergone recent surgery on your head, chest, stomach, or eyes. Always inform your healthcare provider about any pre-existing conditions before testing.

Conclusion

Pulmonary function tests are invaluable tools for assessing respiratory health, diagnosing lung conditions, and monitoring treatment progress. Though they may seem intimidating, these noninvasive tests are straightforward, safe, and provide critical information that helps you and your healthcare team make informed decisions about your lung health. If you have concerns about your breathing or risk factors for lung disease, speak with your doctor about whether pulmonary function testing is right for you.