Pulmonary Function Test Interpretation
Introduction to PFT Interpretation
- The European Respiratory Society recommends a systematic, step-by-step approach to PFT interpretation, starting with the FEV1/VC ratio and considering clinical context 1.
Identifying Obstructive and Restrictive Patterns
- A FEV1/VC ratio < 5th percentile (or <0.70) indicates an obstructive pattern, according to the European Respiratory Society 1, 2.
- A normal or increased FEV1/VC ratio (>85-90%) suggests a restrictive pattern, as stated by the European Respiratory Society 3, 4.
- A normal FEV1/VC ratio but low values for both may indicate poor effort or a mixed pattern, as noted by the European Respiratory Society 4, 5.
Confirming Patterns
- In obstructive patterns, a concave shape on the flow-volume curve is a hallmark of airflow obstruction, as described by the European Respiratory Society 1, 2.
- FEV1 is proportionally more reduced than VC in obstructive patterns, according to the European Respiratory Society 1.
- TLC measurement can help differentiate between emphysema and asthma, with increased TLC indicating hyperinflation, as stated by the European Respiratory Society 4, 5.
Evaluating Restrictive Patterns
- A TLC < 5th percentile is required to confirm restriction, as recommended by the European Respiratory Society 3, 6.
- A convex pattern on the flow-volume curve is characteristic of restrictive patterns, as described by the European Respiratory Society 4, 5.
- Reduced VC alone does not prove restriction, as only 50% of cases with low VC have low TLC, as noted by the European Respiratory Society 3, 5.
Assessing Severity
- FEV1 % predicted is used to assess severity, with mild, moderate, and severe categories based on FEV1, as recommended by the European Respiratory Society 7, 8.
- FEV1 poorly correlates with symptoms in individual patients, as stated by the European Respiratory Society 8.
Evaluating DLCO
- Low DLCO indicates parenchymal disease, emphysema, or vascular involvement, as described by the European Respiratory Society 9, 8.
- DLCO is an important predictor of mortality, as noted by the European Respiratory Society 8.
- Hemoglobin value and altitude should be adjusted for when interpreting DLCO, as recommended by the European Respiratory Society 9.
Checking Bronchodilator Response
- A significant response to bronchodilators is defined as an increase in FEV1 or FVC of >12% and >200 mL, as stated by the European Respiratory Society 7.
- The absence of a response does not rule out clinical benefit from bronchodilator therapy, as noted by the European Respiratory Society 7.