Pulmonary Function Tests (PFTs): Results Explained

What are Pulmonary Function Tests?

Pulmonary Function Tests (PFTs) are a group of breathing tests that measure how well your lungs work. They assess lung size, airflow, and how effectively oxygen moves into your bloodstream.

Think of PFTs as a stress test for your lungs. Just as a treadmill test evaluates your heart's response to exertion, PFTs evaluate your lungs' capacity to move air and exchange gases.

What PFTs measure:

Spirometry (most common test):

• FVC (Forced Vital Capacity): Total air you can exhale forcefully
• FEV1 (Forced Expiratory Volume in 1 second): Air exhaled in first second
• FEV1/FVC ratio: Comparison of these values (identifies obstruction)
• PEF (Peak Expiratory Flow): Maximum speed of exhalation

Lung volume measurements:

• TLC (Total Lung Capacity): Total air in lungs
• RV (Residual Volume): Air remaining after full exhalation
• FRC (Functional Residual Capacity): Air in lungs at rest

Diffusion capacity:

• DLCO (Diffusing capacity of lung for carbon monoxide): How well oxygen moves into blood

Understanding Your Results

Spirometry: The Core Test

Spirometry is the most important and commonly performed PFT. It measures how much air you can exhale and how quickly.

Normal results:

• FVC and FEV1: ≥80% of predicted value (based on age, gender, height, ethnicity)
• FEV1/FVC ratio: 70-75% or higher

Test procedure:

1. Breathe in deeply until lungs are completely full
2. Blast air out as fast and hard as possible
3. Continue exhaling until lungs are empty (6+ seconds)
4. Repeat 3 times to ensure consistent results

Patterns of Abnormality

PFT results show specific patterns that help identify the type of lung problem:

Obstructive Pattern

What it means: Airways are narrowed or blocked, making it hard to exhale air quickly. Air gets trapped in lungs.

Typical findings:

• FEV1: Reduced (＜80% predicted)
• FVC: Normal or mildly reduced
• FEV1/FVC ratio: Low (＜70%)

Common causes:

Restrictive Pattern

What it means: Lungs can't fully expand. Reduced lung volume makes it hard to breathe deeply.

Typical findings:

• FVC: Reduced (＜80% predicted)
• FEV1: Reduced proportionally
• FEV1/FVC ratio: Normal or elevated (＞70%)

Common causes:

Bronchodilator Reversibility Testing

After baseline spirometry, you inhale a bronchodilator medication (albuterol) and repeat the test after 15-20 minutes.

Significant reversibility:

• FEV1 increases ≥12% AND ≥200 mL: Suggests asthma
• Reversible obstruction improves with bronchodilator treatment

No significant reversibility:

• COPD, fixed obstruction
• Other causes of obstruction

When Are PFTs Ordered?

Your Action Plan Based on Results

If PFTs are completely normal:

• No evidence of lung dysfunction
• Continue healthy respiratory habits:
  • Don't smoke (or quit if you smoke)
  • Avoid lung irritants when possible
  • Stay physically active
  • Get recommended vaccinations (flu, pneumonia)
• No further PFTs needed unless symptoms develop

If you have obstructive pattern (asthma):

• Confirm reversibility with bronchodilator testing
• Start asthma treatment:
  • Inhaled bronchodilators (albuterol for quick relief)
  • Inhaled steroids for long-term control
  • Avoid asthma triggers
• Monitor with peak flow meter at home
• Repeat PFTs to assess treatment response

If you have obstructive pattern (COPD):

• Confirm diagnosis (no significant reversibility)
• Start COPD treatment:
  • Smoking cessation if you smoke (essential!)
  • Bronchodilators (long-acting inhaled medications)
  • Pulmonary rehabilitation
  • Vaccinations (flu, pneumonia, COVID-19)
• Annual PFTs to monitor progression
• Oxygen therapy if indicated (based on oxygen saturation)

If you have restrictive pattern:

• Further evaluation to identify cause:
  • High-resolution CT chest
  • Autoimmune testing if indicated
  • Occupational exposure history
  • Physical examination for chest wall abnormalities
• Treatment depends on underlying cause
• May need referral to pulmonologist

If PFTs are borderline or inconclusive:

• Repeat testing may be recommended
• Additional testing:
  • Bronchial provocation testing (methacholine challenge) for suspected asthma
  • Lung volume measurements (body plethysmography)
  • Diffusion capacity (DLCO) measurement
  • Exercise testing

Preparing for Your PFT

Before the test:

• No smoking for at least 1 hour before test (preferably 4-6 hours)
• No heavy exercise for 30 minutes before test
• Avoid large meals before test (full stomach limits breathing)
• Wear loose clothing that doesn't restrict chest movement
• Follow your doctor's instructions about holding respiratory medications
  • Short-acting bronchodilators (albuterol): Usually hold 4-6 hours
  • Long-acting bronchodilators: Usually hold 12-24 hours
  • Inhaled steroids: Usually continue as prescribed

During the test:

• You'll sit upright and wear nose clips
• You'll breathe through a mouthpiece
• The technician will coach you through each maneuver
• Effort matters—give your best effort for accurate results
• You may feel lightheaded or temporarily short of breath (normal)

After the test:

• You can return to normal activities immediately
• Results are usually available the same day
• Your doctor will review results with you

Common Questions

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Disclaimer: This information is for educational purposes only and does not constitute medical advice. Always consult your healthcare provider to interpret your PFT results and determine appropriate management.