What are pulmonary function tests?

What Are Lung Function Tests?

Lung function tests (also called pulmonary function tests or PFTs) are a group of objective measurements that assess how well your lungs move air in and out, how much air they can hold, and how efficiently they transfer oxygen into the bloodstream 1.

Core Components of Pulmonary Function Testing

The main tests that comprise a complete pulmonary function assessment include:

Spirometry with Flow-Volume Loop

• Measures how much air you can forcibly exhale and how quickly
• Key parameters include:
  • FEV₁ (Forced Expiratory Volume in 1 second): Volume of air exhaled in the first second 1
  • FVC (Forced Vital Capacity): Total volume of air you can forcibly exhale 1
  • FEV₁/FVC ratio: Helps distinguish obstructive from restrictive patterns 1
  • PEF (Peak Expiratory Flow): Maximum flow rate during exhalation 1

Lung Volume Measurements

• Determines the total capacity and subdivisions of lung volumes 2
• Includes:
  • TLC (Total Lung Capacity): Total amount of air in lungs after maximal inspiration 1
  • RV (Residual Volume): Air remaining after maximal exhalation 1
  • FRC (Functional Residual Capacity): Air in lungs at rest 1
  • VC (Vital Capacity): Maximum amount of air that can be exhaled 2

Diffusing Capacity (DL,CO)

• Measures how efficiently oxygen transfers from the lungs into the bloodstream using carbon monoxide as a tracer gas 1, 3
• Also called transfer factor
• Critical for detecting problems with the alveolocapillary membrane 2

Additional Specialized Tests

• Bronchial challenge testing: Assesses airway hyperresponsiveness 4
• Exercise testing: Evaluates respiratory function during physical stress 4
• Respiratory muscle strength testing: Measures inspiratory and expiratory muscle function 5

Clinical Applications

PFTs serve multiple critical purposes in respiratory medicine 3, 6:

• Diagnosis: Helps identify obstructive diseases (asthma, COPD), restrictive diseases (interstitial lung disease), and can even detect cardiac or neuromuscular conditions 3
• Disease severity assessment: Quantifies the degree of impairment 6
• Treatment monitoring: Tracks response to therapy and disease progression 6
• Preoperative evaluation: Assesses surgical risk in patients undergoing major procedures 2
• Disability assessment: Provides objective data for functional capacity 4

Interpretation Framework

The interpretation of lung function tests involves two distinct tasks 1:

1. Laboratory-level interpretation: Classification of values against reference populations and quality assessment—typically the responsibility of the laboratory director 1

2. Clinical integration: Incorporating results into diagnosis, treatment planning, and prognosis within the context of individual patient care—the responsibility of the ordering physician 1

Critical Quality Considerations

High-quality PFT results depend heavily on well-trained, motivated technicians and rigorous quality control programs 1. The testing requires:

• Proper equipment calibration with daily checks 1
• Continuous technician performance monitoring with feedback 1
• Use of appropriate reference values matched to the patient's age, sex, and ethnicity 1
• Consistent interpretive strategies to avoid false conclusions about disease progression 1

Important Caveats

• PFTs are rarely diagnostic on their own (except for asthma) but serve as valuable adjuncts to clinical assessment 6
• Results must be interpreted in the context of the clinical presentation, not in isolation 3
• Reference values should come from populations using similar equipment and including the appropriate demographic characteristics 1
• Recent updates emphasize that racial/ethnic differences in lung function reflect socioeconomic factors and health disparities rather than biological differences 7