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# Reading spirometry: obstructive or restrictive?

- Interpretation

The patient blows out as hard and as long as possible; how much and how fast air leaves the lungs shows whether airways are narrow or lungs are small.

Updated Nov 13, 2026

## Key points

- Obstruction: FEV1/FVC below the lower limit of normal, or below 0.70 in COPD guidelines (post-bronchodilator).
- Restriction is only suggested by spirometry (low FVC, normal or high ratio); it is confirmed by a low total lung capacity.
- Significant bronchodilator response: FEV1 or FVC rises by at least 12% and 0.2 L (newer standards use more than 10% of predicted).
- Obstruction severity by FEV1 % predicted (GOLD): 80% or more mild, 50–79% moderate, 30–49% severe, under 30% very severe.
- Low DLCO with obstruction suggests emphysema; normal DLCO with obstruction suggests asthma; low DLCO with restriction suggests interstitial disease.

On this page

- The basics Key points
- What it is
- Reference values and concepts
- Reading it step by step
- Patterns and common mistakes
- Next step
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Spirometry patterns (with lung volumes and DLCO when available)

- Study Test yourself

- Connections Connections

## What it is

Spirometry measures how much air a person can blow out after a full breath in, and how fast. The forced vital capacity (FVC) is the total volume exhaled with maximal effort; the forced expiratory volume in one second (FEV1) is the part that leaves in the first second; their ratio, FEV1/FVC, tells the two main patterns apart. In obstruction (asthma, COPD, bronchiectasis) narrowed airways slow the flow, so FEV1 falls more than FVC and the ratio is low; the flow–volume loop has a scooped, concave expiratory limb. In restriction (interstitial lung disease, chest wall deformity, obesity, neuromuscular weakness) the lungs hold less air, so both volumes fall together and the ratio is normal or high; spirometry can only suggest restriction, which is confirmed by a total lung capacity below normal on lung volume testing. Each value is compared with a predicted value for age, sex, height and ethnicity, ideally using the lower limit of normal (the 5th percentile) rather than fixed cut-offs. A bronchodilator test shows whether obstruction is reversible, which favours asthma. Diffusing capacity (DLCO) adds whether gas transfer across the alveoli is affected. A result is only as good as the effort: the report must show acceptable and repeatable manoeuvres before it is read.

## Reference values and concepts

- FEV1/FVC normally about 0.75–0.85 in young adults and falls with age; a fixed 0.70 overcalls obstruction in older and undercalls it in younger people.
- Normal FEV1 and FVC: about 80% of predicted or more, or above the lower limit of normal (the 5th percentile of a reference population).
- Acceptable manoeuvre: a fast start, no cough or leak, and exhalation to a plateau or for about 6 seconds in adults.
- Repeatable: at least three acceptable manoeuvres, with the two best FVC and FEV1 within about 0.15 L of each other.
- Total lung capacity below about 80% of predicted (or below the lower limit) confirms restriction.
- DLCO is low in emphysema, interstitial lung disease, pulmonary vascular disease and anaemia; often normal or high in asthma.

## Reading it step by step

- Check identity, age, height, sex and the reference equations — predicted values depend on them; a wrong height shifts every percentage.
- Check quality: acceptable starts, no cough, a plateau and repeatable curves — a poor effort mimics restriction or obstruction.
- Read FEV1/FVC first — below the lower limit of normal (or 0.70) means obstruction; normal or high means look at FVC.
- If obstructed, grade it by FEV1 % predicted — severity guides treatment and follow-up.
- Read the post-bronchodilator values — a rise of at least 12% and 0.2 L favours asthma; persistent obstruction supports COPD.
- If the ratio is normal but FVC is low, suspect restriction — confirm with lung volumes (total lung capacity) before calling it.
- Low FEV1/FVC and low FVC together: obstruction with air trapping or a mixed defect — lung volumes separate the two.
- Look at the flow–volume loop shape — scooped in obstruction, narrow and tall in restriction, flattened limbs in upper airway obstruction.
- Add DLCO if available — it separates emphysema from asthma, and interstitial from chest wall or neuromuscular restriction.
- Fit the result to the patient — symptoms, smoking, exposures and imaging turn a pattern into a diagnosis.

## Spirometry patterns (with lung volumes and DLCO when available)

| Pattern | FEV1/FVC | FVC | Total lung capacity | DLCO | Examples |
| --- | --- | --- | --- | --- | --- |
| Normal | Normal | Normal | Normal | Normal | — |
| [Obstructive, reversible](https://durgical.com/en/conditions/asthma/) | Low; improves after bronchodilator | Normal or low | Normal or high | Normal or high | Asthma |
| [Obstructive, fixed](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/) | Low; little change after bronchodilator | Normal or low (air trapping) | Normal or high | Low in emphysema | COPD, bronchiectasis, cystic fibrosis |
| [Restrictive, lung tissue](https://durgical.com/en/conditions/interstitial-lung-disease/) | Normal or high | Low | Low | Low | Interstitial lung disease, sarcoidosis |
| [Restrictive, outside the lung](https://durgical.com/en/conditions/obesity-hypoventilation-syndrome/) | Normal or high | Low | Low | Normal | Obesity, kyphoscoliosis, neuromuscular weakness |
| Mixed | Low | Low | Low | Variable | Combined disease, such as COPD with fibrosis |
| [Upper airway obstruction](https://durgical.com/en/conditions/subglottic-stenosis/) | Often normal or low | Normal | Normal | Normal | Tracheal or subglottic stenosis: flattened loop |

## Patterns and common mistakes

- Reading a submaximal effort as restriction: check the curves and the repeatability before the numbers.
- Calling restriction from a low FVC alone; air trapping in obstruction also lowers FVC, so lung volumes are needed.
- Diagnosing COPD on a pre-bronchodilator test; COPD needs post-bronchodilator obstruction.
- A normal spirometry between attacks does not exclude asthma; repeat when symptomatic, check peak-flow variability or a challenge test.
- Flattened inspiratory and expiratory limbs suggest fixed upper airway obstruction (such as tracheal stenosis), easy to miss on numbers alone.
- Neuromuscular weakness: a low vital capacity that falls further lying down warns of respiratory failure.

## Next step

- Obstruction: confirm with post-bronchodilator values and start or adjust treatment for asthma or COPD; review inhaler technique.
- Suggested restriction: request full lung volumes and DLCO, and chest imaging (high-resolution CT if interstitial disease is possible).
- Flattened loop or stridor: arrange urgent airway assessment by ENT or pulmonology.
- Falling vital capacity in neuromuscular disease, or hypoxia or hypercapnia: call a senior and check blood gases.
- Poor-quality test: repeat it with coaching rather than reporting it; refer unexplained results to pulmonology.
- Repeat spirometry to follow the disease and the response to treatment, at intervals set by the diagnosis.

## Memory aid

Ratio first, then FVC, then TLC: the ratio finds obstruction, a low FVC raises restriction, and only a low TLC proves it.

## Test yourself

Think of the answer, then tap the question to see it.

## FEV1 55% predicted, FVC 90% predicted, FEV1/FVC 0.50, little change after a bronchodilator, in a 65-year-old smoker. What is the pattern?

Fixed obstruction of moderate severity (FEV1 50–79% predicted), consistent with COPD in a smoker. DLCO and imaging help to assess emphysema.

## FEV1 65% and FVC 62% predicted with FEV1/FVC 0.86. What does this suggest and what confirms it?

A restrictive pattern: both volumes are low with a normal-high ratio. Full lung volumes confirm it if total lung capacity is low; DLCO then separates lung tissue from chest wall or muscle causes.

## After salbutamol, FEV1 rises from 2.0 L to 2.4 L. Is this a significant response?

Yes: a rise of 0.4 L and 20%, above the threshold of at least 12% and 0.2 L. Marked reversibility favours asthma.

## The flow–volume loop shows flattened inspiratory and expiratory limbs. What does it suggest?

Fixed upper airway obstruction, such as tracheal or subglottic stenosis or a tumour. It needs urgent airway assessment, especially with stridor.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/clinical-skills/reading-spirometry-obstructive-or-restrictive/)

## Elsewhere in DurgiPedia

- [Lung volumes, capacities and spirometry](https://durgical.com/en/physiology/lung-volumes-capacities-and-spirometry/)
- [Lung and chest wall compliance](https://durgical.com/en/physiology/lung-and-chest-wall-compliance/)
- [Hypoxemic and hypercapnic respiratory failure](https://durgical.com/en/physiology/hypoxemic-and-hypercapnic-respiratory-failure/)
- [Reading a chest X-ray step by step](https://durgical.com/en/radiology/reading-a-chest-x-ray-step-by-step/)

## Connections

## Related 4

- [Peak flow and inhaler technique](https://durgical.com/en/clinical-skills/peak-flow-and-inhaler-technique/)
- [Arterial blood gas: worked cases for the station](https://durgical.com/en/clinical-skills/arterial-blood-gas-worked-cases-for-the-station/)
- [Bronchoscopy](https://durgical.com/en/clinical-skills/bronchoscopy/)
- [Exercise and pharmacological stress testing](https://durgical.com/en/clinical-skills/exercise-and-pharmacological-stress-testing/)

## Related conditions 11

- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Bronchiectasis](https://durgical.com/en/conditions/bronchiectasis/)
- [Sarcoidosis](https://durgical.com/en/conditions/sarcoidosis/)
- [Myasthenia gravis](https://durgical.com/en/conditions/myasthenia-gravis/)
- [Amyotrophic lateral sclerosis](https://durgical.com/en/conditions/amyotrophic-lateral-sclerosis/)
- [Obesity hypoventilation syndrome](https://durgical.com/en/conditions/obesity-hypoventilation-syndrome/)
- [Subglottic stenosis](https://durgical.com/en/conditions/subglottic-stenosis/)
- [Pulmonary hypertension and cor pulmonale](https://durgical.com/en/conditions/pulmonary-hypertension-and-cor-pulmonale/)

## In Pharmacology 4

- [Salbutamol](https://durgical.com/en/pharmacology/salbutamol/)
- [Beta-2 adrenergic agonists](https://durgical.com/en/pharmacology/classes/beta-2-adrenergic-agonists/)
- [Ipratropium bromide](https://durgical.com/en/pharmacology/ipratropium-bromide/)
- [Inhaled corticosteroids](https://durgical.com/en/pharmacology/classes/inhaled-corticosteroids/)

[← All clinical skills](https://durgical.com/en/clinical-skills/)

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: [Spirometry](https://www.ncbi.nlm.nih.gov/books/NBK560526/) (StatPearls (NCBI Bookshelf), 2023); [Pulmonary Function Tests](https://www.ncbi.nlm.nih.gov/books/NBK482339/) (StatPearls (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/clinical-skills/reading-spirometry-obstructive-or-restrictive/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-skills/reading-spirometry-obstructive-or-restrictive/