Back to Topics
Physiology
Pulmonary Function Test (PFT) Interpretation
Added by Dr. Andrew · Last updated 2024-01-15
Overview
PFT interpretation is a core clinical skill for pulmonologists. A systematic approach to spirometry, lung volumes, and DLCO allows accurate characterization of obstructive, restrictive, and mixed patterns, and guides diagnosis and management.
Key Points
- 1Obstructive: FEV1/FVC <0.70 (or <LLN); FEV1 reduced; FVC normal or reduced
- 2Restrictive: TLC <80% predicted (or <LLN); FEV1/FVC normal or increased; FVC reduced
- 3Mixed: FEV1/FVC <0.70 AND TLC <80% — both obstructive and restrictive components
- 4DLCO: measures gas transfer; reduced in emphysema, ILD, pulmonary vascular disease, anemia
- 5Bronchodilator response: ≥12% AND ≥200 ml increase in FEV1 or FVC = significant reversibility
- 6Severity of obstruction: FEV1 ≥80% (mild), 50–79% (moderate), 30–49% (severe), <30% (very severe)
Clinical Pearls
- Low DLCO with normal spirometry: think emphysema, pulmonary vascular disease, anemia
- Elevated DLCO: polycythemia, pulmonary hemorrhage (Goodpasture, DAH), left-to-right shunt
- Pseudo-restriction: air trapping in severe COPD can reduce FVC, mimicking restriction — check TLC
- Variable extrathoracic obstruction (VCD): flattened inspiratory loop; variable intrathoracic: flattened expiratory loop
Board High-Yield
Exam Focus- Restriction confirmed by TLC <80% — not by FVC alone
- DLCO reduced in: emphysema, ILD, PAH, PE, anemia
- DLCO elevated in: polycythemia, pulmonary hemorrhage, early CHF
- Bronchodilator response: ≥12% AND ≥200 ml (both criteria must be met)
- Fixed upper airway obstruction: flattened both inspiratory and expiratory loops
ABIM Exam Weight
4%
Respiratory Physiology & PFTs represents approximately 4% of the PCCM certification exam.