PFTs

Pulmonary Function Tests (PFTs) – Peter Edmonds

PFTs should rarely be ordered in inpatient setting as acute illness can lead to suboptimal results.

Full PFTs include and can be ordered as the following:

  • Spirometry: FVC, FEV1, with or without bronchodilator
    • Outpatient evaluation of patients with new shortness of breath, chronic cough, or upper airway obstruction
  • Plethysmography: TLC, RV
    • Evaluation of restrictive diseases (ILD, neuromuscular disease) and/or hyperinflation (COPD, asthma)
  • Diffusion (DLCO) can be added to plethysmography.
    • Full PFTs' = Spirometry + Plethysmography + DLCO

 

Tips for ordering:

  • Initial diagnostic workup
    • Order full PFTs with bronchodilator challenge
  • Chronic Lung disease:
    • Order spirometry only to track FEV1/FVC over time +/- DLCO to evaluate ILD

 

Interpretation:

  • 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 reduced as well, but FEV1/FVC ratio should be 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
    • DDx if DLCO decreased: COPD, CF, bronchiectasis
    • DDx if DLCO normal: 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:
    • DDx if DLCO decreased:  ILD
    • DDx if DLCO normal: pleural disease, chest wall (e.g. obesity, scoliosis), Neuromuscular disorders
  • Decreased DLCO:
    • If PFTs otherwise normal, DDx includes pulmonary vascular disease, pulmonary edema, or mixed obstructive/restrictive disease (with pseudo-normalization of other PFTs)