Full pulmonary function tests
Also known as: lung function tests, gas transfer, lung volumes, body plethysmography
Spirometry plus measurements it cannot make: the total volume of the lungs including the air that cannot be blown out, and how easily gas crosses from the air sacs into blood (gas transfer, DLCO). Together they classify almost any lung disease.
- Abbreviations
- PFTs, PFT
- Kind
- Physiological or functional test
- Categories
- Respiratory
- Specimen
- No specimen
- Method
- Spirometry, Body plethysmography, Gas transfer (DLCO)
What it measures
| Measure | What it tells you |
|---|---|
| Total lung capacity and residual volume | Measured in a sealed booth (plethysmography) or by gas dilution; high in emphysema (air trapping), low in fibrosis. |
| Gas transfer (DLCO) | How much of a trace of carbon monoxide crosses into blood in one breath; reduced in emphysema, fibrosis and pulmonary vascular disease, raised in lung bleeding. |
| Flow-volume loop | The shape reveals upper airway obstruction and the site of narrowing. |
| Respiratory muscle pressures | For suspected neuromuscular weakness. |
Why it is ordered
- Unexplained breathlessness with normal spirometry
- Interstitial lung disease and sarcoidosis
- Assessing fitness for lung resection or chemotherapy (bleomycin)
- Neuromuscular disease affecting breathing
- Grading emphysema
How it is done
Sitting in a clear booth breathing through a mouthpiece with a nose clip through a series of manoeuvres, about an hour.
Preparation. As for spirometry; avoid smoking for 24 hours because carbon monoxide affects gas transfer.
Reading the result
| Finding | Usual meaning |
|---|---|
| Obstruction with high residual volume and low DLCO | Emphysema |
| Restriction with low DLCO | Pulmonary fibrosis or other interstitial disease |
| Restriction with normal DLCO | Chest wall, obesity or muscle weakness rather than lung parenchyma |
| Low DLCO with normal volumes | Pulmonary vascular disease, early fibrosis, anaemia |
Reference ranges vary by laboratory, method, age, sex and clinical context; a result is read against the person, not a table.
Limitations
Anaemia lowers DLCO; results are compared with predicted values that depend on age, sex, height and ethnicity.
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.