What is a lung function test?

Lung function tests (respiratory function tests or spirometry) are a series of tests used to assess lung capacity and their function to help classify the type of respiratory disease in an individual.

Components of a lung function test include:

  • Forced vital capacity (FVC)
  • Forced expiratory volume in 1 second (FEV1)
  • FEV1/FVC ratio
  • Pre and post-bronchodilator measurements

When would you need a lung function test?

A lung function test may be requested by your doctor for symptoms such as shortness of breath (dyspnoea), cough or wheezing.

How is a lung function test performed?

Lung function tests involve breathing into a mouthpiece, which is connected to a small machine via some tubing. You will be required to breathe in and out as deeply as possible, and then as fast and as forcefully as possible. The test may make you feel temporarily short of breath, but is otherwise harmless.

More sophisticated testing such as gas transfer tests require the patient to breathe into a closed system, via a tight-fitting face mask.

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Lung function test results explained

Lung function tests usually aim to distinguish between two typs of lung disease; obstructive and restrictive.


Obstructive lung diseases include:

  • Asthma
  • Emphysema
  • Chronic bronchitis
  • Cystic fibrosis
  • Chronic obstructive pulmonary disease (COPD)


Restrictive lung diseases include:

  • Pulmonary fibrosis
  • Sarcoidosis
  • Obesity hypoventilation syndrome
  • Scoliosis

The FEV1/FVC ratio is decreased in obstructive lung disease, and usually increased in restrictive patterns of lung disease.

Related specialists

Related procedures

  • Bronchoscopy

Related tests

Also known as

  • Respiratory function tests
  • RFTs
  • Pulmonary function tests (PFTs)
  • Spirometry


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This article is for informational purposes only and should not be taken as medical advice. If in doubt, HealthEngine recommends consulting with a registered health practitioner.