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Pulmonary Function Tests (PFTs)

Peter Edmonds

Full PFTs include:

  • Spirometry: FVC, FEV1, with or without bronchodilator

    • Patients with new shortness of breath, chronic cough, or upper airway obstruction
  • Plethysmography: TLC, RV

    • Evaluation of restrictive diseases (ILD, neuromuscular) or hyperinflation (COPD, asthma)
  • Diffusion (DLCO) can be added to plethysmography

  • 'Full PFTs' = Spirometry + Plethysmography + DLCO

Tips for ordering:

  • Initial diagnostic workup: Full PFTs with bronchodilator challenge

  • Chronic Lung disease: Spirometry to track FEV1/FVC over time ± DLCO to evaluate ILD


  • Distinguish between obstructive and restrictive disease

    • FEV1/FVC \< 0.7 indicates obstructive disease

      • Normal to increased FVC & TLC is consistent with isolated obstructive disease
    • TLC \< 80% is diagnostic of restrictive disease

      • Reduced FVC is suggestive, but not diagnostic of restrictive disease

      • FEV1 commonly too but FEV1/FVC ratio is normal in isolated restrictive disease

    • Decreased FEV1/FVC and TLC suggests a mixed obstructive and restrictive picture

  • Assess DLCO -- abnormal is \<75%

    • Decreased DLCO can help differentiate between causes of obstructive or restrictive PFTs

Causes of common abnormalities:

  • Obstruction

    • Decreased DLCO: COPD, CF, bronchiectasis

    • Normal DLCO: asthma, early stages of COPD or CF

      • Asthma: spirometry may be normal, +bronchodilator response (an increase in FEV1 by 12% and 200ml after bronchodilator), +methacholine challenge
    • Though we use FEV1/FVC to diagnose, we track disease severity using FEV1

  • Restriction:

    • Decreased DLCO: ILD

    • Normal DLCO: pleural disease, chest wall (obesity, scoliosis), neuromuscular disorders

  • Decreased DLCO: If PFTs otherwise normal consider pulmonary vascular disease, pulmonary edema, or mixed obstructive/restrictive disease (pseudo-normalization of PFTs)

Last update: 2022-06-26 16:08:18