Pulmonary Function Tests (PFTs) – Purpose, Types, and Results Explained

Introduction

Pulmonary Function Tests (PFTs) are a group of non-invasive diagnostic tests that measure how well your lungs are working. These tests assess lung volume, capacity, flow rates, and gas exchange, helping doctors diagnose conditions like asthma, COPD, pulmonary fibrosis, and other respiratory disorders.

With over 339 million people worldwide suffering from asthma (WHO) and COPD being the third leading cause of death globally (GOLD Report), PFTs play a crucial role in early detection and management. In this comprehensive guide, we’ll explore the different types of PFTs, how they work, who needs them, and what to expect during testing.

What Are Pulmonary Function Tests (PFTs)?

Pulmonary Function Tests evaluate how well your lungs take in and release air and how efficiently they transfer oxygen into your bloodstream. These tests help:

Diagnose lung diseases
Monitor disease progression
Assess treatment effectiveness
Evaluate lung function before surgery

Why Are PFTs Important?

Early Detection: Identifies lung issues before symptoms worsen.
Accurate Diagnosis: Differentiates between obstructive (e.g., asthma, COPD) and restrictive (e.g., pulmonary fibrosis) lung diseases.
Treatment Guidance: Helps doctors adjust medications or therapies.

Types

There are several types of PFTs, each measuring different aspects of lung function:

1. Spirometry

Purpose: Measures how much and how quickly you can exhale air.
Key Metrics:

Forced Vital Capacity (FVC): Total air exhaled forcefully.
Forced Expiratory Volume (FEV1): Air exhaled in the first second.
FEV1/FVC Ratio: Helps differentiate between obstructive and restrictive diseases.

Conditions Diagnosed: Asthma, COPD, chronic bronchitis.

2. Lung Volume Tests

Purpose: Measures total lung capacity (TLC) and residual volume (RV).
Methods:

Body Plethysmography: Uses a sealed chamber to measure lung volumes.
Nitrogen Washout: Tracks nitrogen levels as you breathe pure oxygen.

Conditions Diagnosed: Pulmonary fibrosis, sarcoidosis.

3. Diffusion Capacity Test (DLCO)

Purpose: Evaluates how well oxygen passes from the lungs into the blood.
How It Works: You inhale a small amount of carbon monoxide (CO), and the test measures how much is absorbed.

Conditions Diagnosed: Emphysema, pulmonary hypertension.

4. Bronchial Provocation Test

Purpose: Checks for asthma by measuring airway sensitivity.
Procedure: You inhale methacholine or perform exercise to trigger airway narrowing.

5. Six-Minute Walk Test (6MWT)

Purpose: Assesses exercise tolerance in chronic lung diseases.

Who Needs a Pulmonary Function Test?

Your doctor may recommend PFTs if you have:
✔ Chronic cough or shortness of breath
✔ Wheezing or chest tightness
✔ A history of smoking
✔ Exposure to lung irritants (asbestos, chemicals)
✔ Pre-surgical evaluation

High-Risk Groups:

Smokers & ex-smokers
People with a family history of lung disease
Workers exposed to industrial pollutants

How to Prepare for a PFT

To ensure accurate results:

Avoid smoking for at least 6 hours before the test.
Skip heavy meals 2 hours prior.
Wear loose clothing for unrestricted breathing.
Inform your doctor about medications (some may need to be paused).

What to Expect During the Test

Spirometry: You’ll blow into a mouthpiece connected to a spirometer.
Lung Volume Test: You’ll sit in a clear booth and breathe normally.
Diffusion Capacity Test: You’ll inhale a harmless gas and hold your breath briefly.

The test is painless and typically takes 30–90 minutes.

Understanding PFT Results

Results are compared to normal values based on age, sex, height, and ethnicity.

Test	Normal Range	Abnormal Indications
FEV1/FVC Ratio	> 0.70 (70%)	< 0.70 suggests COPD/asthma
FVC	80–120% predicted	Low in restrictive diseases
DLCO	75–140% predicted	Low in emphysema, fibrosis

Obstructive vs. Restrictive Patterns:

Obstructive (e.g., COPD, asthma): FEV1/FVC < 70%
Restrictive (e.g., fibrosis): Reduced FVC but normal FEV1/FVC

Benefits of Pulmonary Function Testing

✅ Early Disease Detection – Identifies lung issues before severe symptoms appear.
✅ Personalized Treatment – Helps tailor inhalers, oxygen therapy, or pulmonary rehab.
✅ Surgical Risk Assessment – Determines if lungs can handle anesthesia.

Limitations of PFTs

❌ Not Diagnostic Alone: Requires clinical correlation (e.g., imaging, symptoms).
❌ Effort-Dependent: Poor technique can skew results.
❌ Not for Everyone: Severe heart conditions may limit testing.

Frequently Asked Questions (FAQs)

1. Are PFTs safe?

Yes, they are non-invasive and low-risk. Some may feel lightheaded from deep breathing.

2. Can children undergo PFTs?

Yes, specialized pediatric PFTs are available for kids as young as 5.

3. How often should PFTs be done?

Depends on the condition—annually for COPD, periodically for asthma control.

4. Do PFTs hurt?

No, but some may feel short of breath during forced exhalation.

Conclusion

Pulmonary Function Tests are essential for diagnosing and managing lung diseases. Whether you’re experiencing breathing difficulties or need pre-surgical clearance, PFTs provide critical insights into lung health. Early detection through these tests can significantly improve treatment outcomes and quality of life.

If you have persistent respiratory symptoms, consult a pulmonologist about getting a PFT. Early diagnosis saves lives!

Pulmonary Function Tests