Pulmonary Function Tests (PFTs)

Jacob Lee

Full PFTs include: Spirometry + Body Plethysmography + DLCO 

  • General indications to order PFTs: unexplained respiratory signs/symptoms, pre-operative risk assessment, diagnosis of COPD, ILD
  • Relative Contraindications: acute MI, decompensated heart failure, PTX, PE, recent surgery, cerebral aneurysm, respiratory infections, hemoptysis

Tips for ordering 

  • Initial diagnostic workup: Full PFTs with bronchodilator challenge
  • Chronic Lung disease: Depends on disease being monitored
    • Asthma: Typically patients will have a PEF meter they can use at home and do not need formal reassessment routinely; can check FEV1 with spirometry
    • COPD: Spirometry to track FEV1/FVC over time ± DLCO
    • Cystic Fibrosis: for flares, will typically only track FEV1 while inpatient, will get repeat full set of PFTs once flare has resolved to establish new baseline
    • ILD: Full PFTs

Interpretation 

  • First, assess validity. The PFT report will state whether the results were consistent and reproducible
  • When looking at specific values, you should look at percent predicted, then if low should look at the actual value and if it falls below the confidence interval to confirm
  • Obstructive Pattern:
    • FEV1/FVC ≤ 0.7 (GOLD) or < LLN (ATS/ERS) indicates obstructive disease
      • A low FVC with an increased TLC is also suggestive of obstructive lung disease, but is not diagnostic per ATS/ERS/GOLD guidelines
      • Increased RV and TLC compared to FVC is suggestive of air trapping
  • Restricted Pattern:
    • TLC < 80% (GOLD) or < LLN (GOLD/ATS/ERS) is diagnostic of restrictive disease
      • Reduced FVC is suggestive, but not diagnostic of restrictive disease
      • FEV1 is commonly low too but FEV1/FVC ratio is normal in isolated restrictive disease
  • Mixed Obstructive and Restrictive Deficits: both low FEV1/FVC and TLC
  • Impaired Gas Exchange: DLCO can help differentiate between pathologies of both obstructive and restrictive lung diseases and may even suggest pathology in the absence of obstructive or restrictive patterns
    • Normal DLCO:
      • Normal DLCO + obstruction: asthma, early COPD/CF
      • Normal DLCO + restriction: pleural disease, chest wall disorders (obesity, scoliosis), neuromuscular disorders (ALS, MG)
    • Low DLCO:
      • Low DLCO + obstruction: emphysema/late COPD, CF, bronchiectasis
      • Low DLCO + restriction: ILD, pneumonitis, lung resection
      • Low DLCO + normal spirometry: anemia, pulmonary hypertension, pulmonary embolism, early ILD, pulmonary edema, mixed obstruction/restriction pattern (pseudonormalization of PFTs)
    • High DLCO: >120-140% or > 95th percentile/ULN (ATS/ERS)
      • L→R shunt, alveolar hemorrhage, polycythemia, asthma
  • Bronchodilator response: indicates reversible airflow obstruction (common in asthma)
    • Positive: Increase in FEV1 and/or FVC by ≥ 12% AND ≥ 200 mL from baseline after bronchodilator administration

Can try to induce bronchospasm/bronchoconstriction with a methacholine challenge to confirm diagnosis of asthma but test is imperfect

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