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Lung Function Test

A lung function test, also known as pulmonary function test (PFT) or spirometry, is a series of non-invasive breathing tests that evaluate how well your lungs function. These tests are often performed by healthcare professionals, such as pulmonologists or respiratory therapists, to assess the presence and severity of respiratory conditions, monitor lung diseases, and guide treatment decisions.

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Everything you need to know

This overall examination of your lungs will assess airway function, the size of your lungs, and the efficiency of gas exchange (the amount of air exhaled and inhaled, and the way the oxygen moves in your lungs).

Lung function tests can help diagnose conditions such as asthma, chronic obstructive pulmonary disease (COPD), interstitial lung disease, and other respiratory disorders. They are useful for assessing the progression of lung diseases and monitoring the effectiveness of treatment.

On average, a complete set of pulmonary function tests, including spirometry and other relevant measurements, may take approximately 30 minutes to an complete, it’s typically an outpatient procedure that is fairly pain-free.


The most common lung function tests include:

  • Spirometry: This test measures the amount and speed of air that can be inhaled and exhaled. The spirometer records various lung volumes and capacities, such as forced vital capacity (FVC) and forced expiratory volume in one second (FEV1).
  • Lung Volume Tests: These tests measure the total amount of air your lungs can hold. One example is plethysmography, which involves sitting in a small, airtight booth and breathing through a mouthpiece.
  • Diffusion Capacity Test: This test assesses how well oxygen passes from the air sacs of the lungs into the bloodstream. It involves inhaling a small amount of a gas (usually carbon monoxide) and measuring how quickly it is taken up by the blood.
  • Peak Expiratory Flow (PEF) Measurement: This simple test measures the maximum speed at which you can exhale air. It is often used to monitor asthma and other respiratory conditions.


Prior to beginning a lung function test, you may have an initial appointment with the doctor.

If they suggest that you should have a lung function test, you may need to follow certain preparation guidelines to ensure accurate and reliable results. Here are some general guidelines, but it’s essential to follow any specific instructions provided by your healthcare provider:

  • Medications: Inform your healthcare provider about all the medications you are currently taking, including prescription drugs, over-the-counter medications, and supplements. In some cases, your doctor may ask you to adjust your medication schedule before the test.
  • Avoid Smoking: If you are a smoker, it is advisable to refrain from smoking for a certain period before the test. Smoking can affect lung function and may impact the accuracy of the results.
  • Avoid Certain Substances: Avoid consuming substances that can affect lung function, such as caffeine or bronchodilator medications, before the test. Your healthcare provider will provide specific instructions on what substances to avoid and for how long.
  • Fasting: In most cases, there is no need to fast before a lung function test. However, you may be advised to avoid heavy meals, caffeine, or alcohol for a few hours before the test.
  • Comfortable Clothing: Wear loose-fitting clothing that allows you to breathe comfortably. Tight clothing may restrict your ability to take deep breaths during the test.
  • Rest: Get a good night’s sleep before the test and avoid strenuous physical activity on the day of the test. Fatigue and exhaustion can affect your lung function.
  • Bring Your Inhaler: If you use an inhaler for a respiratory condition, bring it with you to the test. Your healthcare provider may want to assess your lung function with and without the use of the inhaler.

These tests are also offered as pre-emptive action. If you’re scheduled to have heart surgery, you may be given a lung function test to assess whether your lungs are strong enough to cope with the operation.


The duration of lung function tests can vary depending on the specific tests being performed and the individual’s ability to cooperate and follow instructions. On average, a complete set of pulmonary function tests, including spirometry and other relevant measurements, may take approximately 30 minutes to an hour.

The specific tests conducted can vary, but here’s a general overview of how the most common lung function tests are performed:


You will be asked to sit comfortably in a chair. A soft clip is placed on your nose to ensure that you breathe only through your mouth. You will be instructed to take a deep breath and then exhale as forcefully and completely as possible into a device called a spirometer.
The test is usually repeated several times to ensure consistent and accurate results.

Lung volume tests

You may be seated inside a small, airtight booth or chamber. You will breathe in and out through a mouthpiece attached to the testing equipment.

Diffusion Capacity Test

You will be asked to breathe in a small amount of a test gas, such as carbon monoxide. The concentration of the gas in the air you exhale is measured to assess how well oxygen moves from your lungs into your bloodstream.

Peak Expiratory Flow (PEF) Measurement:

You will use a handheld device called a peak flow meter. Take a deep breath and then exhale as forcefully as possible into the meter. The meter measures the maximum speed of air as it exits your lungs.


Due to the speed of lung function tests, you’ll receive your results soon after taking the test.

The results of these tests provide valuable information about your lung function, helping healthcare providers diagnose respiratory conditions, monitor disease progression, and tailor treatment plans. The doctor will review the results with you, and you will agree what next steps to take. It might be that they arrange another appointment with you to walk you through the options or they book you in for a further procedure.

How to pay for your treatment

If you’re… paying for yourself

Did you know you don’t need private medical insurance to come to St John & St Elizabeth Hospital? As a self-pay patient, you can access safe, outstanding quality health care at times to suit you.

For scans and tests, as well as to see most consultants, you’ll still need to be referred by a medical professional like your GP, but as a self-pay patient, the process is more straightforward. You won’t need authorisation from an insurance provider, and you’ll have greater choice of consultant and appointment times.

If you’re… insured

St John & St Elizabeth Hospital is approved by all major medical insurance companies. If you have a personal private health insurance policy, or your company provide it for you, you can use it to pay for your care from your initial consultation through to treatment, surgery and aftercare such as physiotherapy. Not all private health insurance plans cover the same things. It’s very important to check exactly what you are covered for with your insurance provider.