No, Pulmonary Function Testing (PFT) and Spirometry Are Not the Same
Spirometry is a component test within the broader category of pulmonary function testing (PFT), not a synonym for it. 1
What Spirometry Measures
Spirometry specifically measures a limited set of parameters related to airflow during forced breathing maneuvers 1:
- Forced vital capacity (FVC) - the total volume exhaled during a forceful breath 1
- Forced expiratory volume in 1 second (FEV1) - the volume exhaled in the first second 1
- FEV1/FVC ratio - used to identify airflow obstruction 1
- Flow-volume curves - graphical representation of expiratory airflow 1
The American Thoracic Society recommends that only FVC, FEV1, and FEV1/FVC need to be routinely reported for spirometry, as most other calculated parameters do not add clinical utility 2.
What Comprehensive PFT Includes
A complete pulmonary function test battery encompasses spirometry plus additional measurements 1:
Lung Volume Measurements
Gas Exchange Assessment
- Diffusing capacity (DLCO) - measures gas exchange across the alveolar-capillary membrane, assessing parenchymal lung disease 1
Critical Limitations of Spirometry Alone
Spirometry alone cannot diagnose restrictive lung disease and has several important limitations 1:
- Cannot distinguish between true restriction and pseudorestriction 1
- Cannot quantify hyperinflation or air trapping 1
- Cannot assess gas exchange abnormalities 1
- Cannot measure static lung volumes 1
Clinical Decision Framework
When Spirometry Alone Is Sufficient
For initial screening and monitoring of obstructive diseases (asthma, COPD), spirometry provides essential measurements 1. The American Thoracic Society notes that spirometry is most useful in the evaluation of obstructive airway disorders 3.
When Comprehensive PFT Is Necessary
Comprehensive PFT is necessary for accurate diagnosis when clinical suspicion exists for 1:
- Interstitial lung disease
- Neuromuscular weakness
- Chest wall disorders
- Unexplained dyspnea with normal spirometry
Common Pitfall to Avoid
The most critical error is assuming that normal spirometry excludes all lung disease. In post-hematopoietic stem cell transplantation surveillance, the American Thoracic Society recommends using "spirometry and, where feasible, static lung volumes and DLCO" because spirometry alone may miss important pulmonary complications 2. This principle applies broadly: when the clinical picture doesn't match spirometry results, comprehensive PFT is warranted 1.