What Is a Pulmonary Function Test (PFT)? Types and Uses

A pulmonary function test (PFT) measures how well the lungs work. The term covers several tests, and spirometry is by far the most common.

Spirometry

The patient takes a full breath in and blows out as hard and fast as possible into a mouthpiece. The spirometer measures:

• FVC (forced vital capacity). Total air exhaled forcefully.
• FEV1. Air exhaled in the first second.
• FEV1/FVC ratio. A key marker of airway obstruction.
• PEF and FEF25–75. Peak and mid-flow rates.

Spirometry can also include SVC (slow vital capacity) and MVV (maximum voluntary ventilation).

Other PFTs

• Lung volumes (body plethysmography or gas dilution): total lung capacity and residual volume.
• Diffusion capacity (DLCO): gas transfer across the lungs.
• Bronchodilator reversibility: spirometry before and after an inhaler.
• Bronchial challenge tests: airway hyper-responsiveness.

When are PFTs ordered?

• Diagnosis of asthma and COPD. See spirometry for asthma and COPD.
• Breathlessness or chronic cough.
• Pre-operative assessment. See PFT for pre-op.
• Occupational lung screening. See occupational screening.
• Monitoring of interstitial lung disease or treatment.

Patient preparation

• Avoid smoking, heavy meals and vigorous exercise beforehand.
• Wear loose clothing.
• Follow instructions about inhalers.
• Inform staff about recent surgery, chest pain or illness.

Equipment

Clinics usually start with a spirometer: the PC-based SPIROEXCELL or the portable SPIROMAX. See the PFT price guide.