FEV1 is indispensable, but incomplete. The mistake is treating it like the whole patient when it is only one (important) dimension of lung physiology. I fact, ATS/ERS explicitly warns against interpreting routine PFTs as a standalone clinical diagnosis or management plan.
For decades, we’ve had an “exclusive relationship” with FEV1. It has earned its place as one of the most important measurements in pulmonary function testing: it’s objective, reasonably reproducible, and foundational to spirometry. Together with FVC and the FEV1/FVC ratio it helps identify ventilatory impairment and track change over time—when test quality is acceptable and the result is interpreted against appropriate reference equations.
The real change is to stop treating FEV1 as a complete description of pulmonary function. It remains indispensable, but it is only part of the picture. In this article, we look at what it can (and cannot) tell us, and why the goal is not to move beyond FEV1, but to break up with FEV1-only thinking.
By América Torres
Why FEV1 remains essential in spirometry
FEV1, or forced expiratory volume in one second, measures the volume exhaled during the first second of a forced expiratory maneuver. Together with FVC (forced vital capacity) and the FEV1/FVC ratio, it is fundamental to spirometry interpretation. FEV1/FVC (or FEV1/VC, using the largest VC available) below lower limit of normal (LLN) indicates an obstructive ventilatory impairment. FEV1 also contributes to the classification of the severity of lung function impairment when interpreted using appropriate reference equations and z-scores.
FEV1 is also useful for monitoring lung function over time. However, limits of natural change over time/uncertainty should be interpreted in relation to test quality, biological variability, the interval between measurements and the individual’s previous results. The point is not to question the value of FEV1. It is to put that value in context.
The limitations of FEV1 interpretation
FEV1 measures airflow, not the entire respiratory system
FEV1 primarily reflects expiratory airflow/flow limitation and does not characterize the full respiratory system (lung volumes, gas transfer, mechanics, or symptoms) on its own. When available, routine lung function testing spans three physiological domains:
- Airflow (spirometry)
- Lung volumes (TLC/RV/FRC)
- Gas transfer (DLCO or Diffusing capacity of the lung for carbon monoxide, also called TLCO)
That distinction matters. A reduced FEV1 and FVC with a normal FEV1/FVC ratio, for example, does not by itself establish restriction. A reduced total lung capacity (TLC) is required to confirm a restrictive ventilatory impairment. If TLC is normal, the pattern may instead represent a non-specific pattern, which can have several possible explanations.
Test quality can change the meaning of the number
FEV1 is among the more reproducible lung function indices, but the reliability of any spirometric result depends on appropriate test performance and quality. Poor effort or an incomplete maneuver can produce results that do not accurately represent an individual’s lung function. That is why spirometry interpretation should begin with test quality, not with the numerical result alone.
FEV1 cannot characterize lung volumes or gas transfer
FEV1 does not directly measure TLC, residual volume (RV), functional residual capacity (FRC), or DLCO. Lung volume measurements can help identify restriction and characterize patterns involving air trapping or hyperinflation. DLCO provides information about alveolar-capillary gas transfer that cannot be obtained from spirometry alone.
Beyond FEV1: What else should be interpreted?
A more complete FEV1 interpretation starts by asking what physiological question remains unanswered.
Spirometry. FEV1, FVC and FEV1/FVC assess airflow and help identify ventilatory patterns.
Lung volumes. TLC can confirm restriction, while RV and other volume relationships can provide additional information about lung volume abnormalities. RV/TLC and FRC/TLC help identify air trapping/hyperinflation, and the method (gas dilution vs. plethysmography) can affect TLC estimates in obstruction.
DLCO (TLCO). Assesses pulmonary gas transfer and adds information that spirometry cannot provide.
Reference values. Results should be interpreted using appropriate reference equations and limits of normal rather than relying on a single fixed percentage of predicted.
Clinical context. PFT interpretation should be complemented by clinical expertise and consideration of biological variability and uncertainty (the final diagnostic/management integration is outside the scope of the technical standard).
Taken together, these considerations support a broader approach. Modern PFT interpretation focuses on using airflow, lung volume and gas transfer measurements to recognize patterns of altered physiology, considering reference ranges, biological variability and uncertainty—not merely reading isolated numbers.
A practical approach to pulmonary function test interpretation
1. Start with test quality
Before interpreting FEV1 or any other value, determine whether the test meets the appropriate ERS/ATS technical and quality requirements. A poor-quality measurement carries greater uncertainty.
2. Interpret the spirometric pattern
Start with the FEV1/FVC ratio and then assess FVC and FEV1. A low FEV1/FVC (or FEV1/VC using the largest VC available) below LLN supports an obstructive ventilatory impairment. A low FVC with a normal FEV1/FVC ratio may suggest restriction, but TLC is needed to confirm it.
3. Add the measurement that answers the next question
When spirometry does not fully explain the physiological pattern, additional testing can provide the missing information. Lung volumes can clarify restriction and other volume abnormalities, while DLCO can assess impaired gas transfer.
4. Interpret the complete PFT profile
The ERS/ATS standard emphasizes that PFT interpretation should integrate physiological patterns with appropriate reference values, biological variability, measurement uncertainty and clinical expertise.
Keep FEV1, just stop asking it to tell the whole story
FEV1 is indispensable—but incomplete; the problem is not FEV1 itself, but overinterpreting FEV1 in isolation rather than using it to classify physiology within a full lung function profile and its uncertainty. For decades, pulmonologists have had an “exclusive relationship” with FEV1. It’s objective and among the more reproducible indices in routine lung function testing, and it remains central to spirometry interpretation alongside FVC and the FEV1/FVC ratio. But ERS/ATS also makes the counterpoint explicit: pulmonary function tests classify physiological patterns and should not be used alone to diagnose a specific pathological condition or to substitute for clinical judgment. It is not about abandoning FEV1 but breaking up with FEV1-only thinking. FEV1 belongs on the team. It just cannot tell the whole story on its own.
A Comprehensive approach to pulmonary function testing
Because routine PFTs assess distinct domains—airflow (spirometry), lung volumes/capacities (typically measured by body plethysmography or gas dilution/washout), and alveolar–capillary gas transfer (DLCO/TLCO)—no single metric captures the full physiological picture. When a comprehensive evaluation is needed, spirometry is complemented by lung volumes and DLCO. When appropriate, oscillometry can provide a broader assessment of lung function.
SCHILLER-GANSHORN offers an integrated portfolio of pulmonary function testing solutions, including SpiroScout for ultrasonic spirometry, PowerCube Body+ for body box plethysmography, PowerCube Diffusion+ for DLCO testing, and tremoflo® for oscillometry.
Discover SCHILLER-GANSHORN’s complete pulmonary function testing solutions and find the right tools for your practice, hospital, or lung function laboratory.
Scientific references
Frequently ssked questions about FEV1 and pulmonary function testing
What does FEV1 tell you about lung function?
FEV1 measures the volume of air a patient can forcefully exhale in the first second of a spirometry maneuver. It is an essential measure of airflow and is interpreted together with FVC and the FEV1/FVC ratio. However, FEV1 alone does not provide a complete assessment of pulmonary function.
Is FEV1 enough to interpret pulmonary function?
No. FEV1 is an important spirometric index of airflow, but it does not assess lung volumes (TLC/RV/FRC) or alveolar–capillary gas transfer (DLCO/TLCO). Depending on the clinical question, clinicians should complement spirometry with lung volumes and DLCO. They may add Oscillometry selectively as an adjunct, particularly when small-airway mechanics are suspected or spirometry is not feasible.
What tests can complement FEV1?
Lung volume measurements (e.g., TLC/RV/FRC, method-dependent) help define restriction and identify air trapping/hyperinflation, while DLCO (TLCO) assesses alveolar–capillary gas transfer. Oscillometry measures respiratory system resistance and reactance during tidal breathing and clinicians can use it selectively as an adjunct to spirometry, particularly when small-airway physiology is suspected or spirometry is not feasible.
Why is FEV1 interpretation not enough on its own?
Because a single metric cannot capture all domains of respiratory physiology. ERS/ATS interpretation focuses on airflow, lung volumes, and gas transfer, using appropriate reference equations and considering test quality, biological variability, and result uncertainty, and it should be complemented by clinical expertise.
What is the difference between spirometry and oscillometry?
Spirometry primarily measures airflow (and dynamic volumes such as FVC) during forced breathing maneuvers, whereas oscillometry measures respiratory system impedance—resistance and reactance—during quiet tidal breathing. They are generally complementary tests, with oscillometry particularly useful when spirometry is not feasible or when distal/small-airway mechanics are suspected. The two tests provide complementary information rather than replacing one another.
When are lung volumes and DLCO needed?
Lung volumes and DLCO are obtained when spirometry alone does not answer the physiological question. Lung volumes (TLC/RV/FRC) confirm or refute restriction and help identify air trapping/hyperinflation, while DLCO/TLCO assesses alveolar–capillary gas transfer.
What should be considered before interpreting FEV1?
Test quality should be assessed first. FEV1 and other spirometric indices should then be interpreted against appropriate reference equations and limits of normal (preferably GLI) while explicitly accounting for biological variability and measurement uncertainty—especially for results near decision thresholds. Clinicians should complement the physiological interpretation with clinical expertise and consideration of the patient’s history and symptoms.