Diagnostics

Pulmonary Function Tests: What to Expect

March 20, 20264 min readDr. Milan Modi

Pulmonary Function Tests (PFTs) are a group of non-invasive tests that measure how well your lungs work. They are essential tools for diagnosing, monitoring, and managing a wide range of respiratory conditions. If your doctor has recommended a PFT, here's everything you need to know.

Why Are PFTs Ordered?

PFTs help diagnose and monitor:

Asthma and COPD

Pulmonary fibrosis and interstitial lung disease

Sarcoidosis

Lung cancer evaluation

Pre-surgical assessment

Occupational lung disease

Monitoring treatment effectiveness

Types of Pulmonary Function Tests

Spirometry

The most common PFT. You breathe into a mouthpiece connected to a spirometer, which measures:

FVC (Forced Vital Capacity): Total air exhaled forcefully

FEV1 (Forced Expiratory Volume in 1 second): Air exhaled in the first second

FEV1/FVC ratio: Key indicator for obstructive vs. restrictive patterns

Lung Volume Measurement

Measures total lung capacity, residual volume, and functional residual capacity using a body plethysmograph or gas dilution technique.

Diffusion Capacity (DLCO)

Tests how well oxygen passes from the air sacs into the bloodstream — important for diagnosing emphysema and pulmonary fibrosis.

Bronchodilator Response Test

Spirometry performed before and after inhaling a bronchodilator to assess reversibility — key for asthma diagnosis.

Methacholine Challenge Test

Used to diagnose asthma when spirometry is normal but symptoms suggest asthma.

How to Prepare

Avoid smoking: for at least 4 hours before the test

Avoid bronchodilators: as directed by your doctor

Wear loose, comfortable clothing

Avoid heavy meals: 2 hours before

Avoid vigorous exercise: on the day of testing

Bring a list of all medications

What Happens During the Test

A technician explains the procedure and fits you with a nose clip

You breathe normally, then take a deep breath and exhale as hard and fast as possible

The test is repeated 3 times to ensure accuracy

Results are compared to predicted values based on your age, height, sex, and ethnicity

Understanding Your Results

Normal: FEV1/FVC ratio ≥ 0.70

Obstructive pattern: (asthma, COPD): Low FEV1/FVC ratio

Restrictive pattern: (fibrosis, obesity): Low FVC with normal ratio

Dr. Modi will explain your results in detail and discuss what they mean for your diagnosis and treatment plan.

PFTs are available at Dr. Modi Hospital, Athwa Gate, Surat. The test is painless, takes about 30–45 minutes, and provides invaluable information about your lung health.