Spirometry and lung function tests: what to expect, a review

A breathing test called spirometry is a test used to check how well the lungs are working. Knowing what happens during the test, and how to get ready, can make it less worrying. This article explains lung function tests, using information from MedlinePlus, the NHS, the US CDC and the World Health Organization (WHO).

1. Introduction

Lung function tests, also called pulmonary function tests, measure how well your lungs and airways work. Doctors use them together with other information to diagnose and keep track of lung conditions ^[1]. Most involve breathing into a mouthpiece connected to a measuring device. The results show how much air your lungs can hold, how easily air moves in and out, and how well oxygen passes into the blood ^[1].

2. Main types of test

MedlinePlus describes several kinds of lung function test ^[1]:

• Spirometry. This is the most commonly used test. It measures how much air you can breathe out and how quickly you can push it out.
• Lung volume testing (body plethysmography). This is the most accurate way to measure how much air your lungs can hold, including the air that stays in the lungs after a full breath out. It is often done sitting inside a small, clear, airtight room.
• Diffusion capacity testing. This checks how well the lungs move oxygen into the blood. It uses a very small, safe amount of a gas called carbon monoxide.
• Exercise tests. These look at lung performance during activity. They include the six-minute walk test and cardiopulmonary exercise testing, which watches breathing and heart function while you pedal a bike or walk on a treadmill.

3. Why you might need one

Your doctor may suggest a test if you have ^{[1, 2]}:

• Shortness of breath, wheezing, a lasting cough, chest tightness or an abnormal chest X-ray
• A known lung condition that needs to be tracked, to see whether treatment is helping
• Exposure to harmful substances, such as asbestos or radiation
• A planned operation, to check fitness for surgery

The NHS adds that spirometry may be offered to people over 55 who smoke as part of lung cancer screening, or to people at risk of lung disease ^[2]. Spirometry helps doctors find out whether symptoms come from conditions such as asthma, COPD or pulmonary fibrosis, another long-term lung condition ^[2].

For some conditions it is the key test. WHO says COPD is confirmed with spirometry, and that the test is often unavailable in low- and middle-income countries, so the diagnosis may be missed ^[4]. The CDC explains that in suspected asthma, spirometry tests how much air you breathe out after a very deep breath, before and after you use asthma medicine ^[3].

4. How to prepare

Follow the instructions you are given, and ask your clinic if anything is unclear. Common advice includes ^{[1, 2]}:

• Wear loose, comfortable clothing.
• Avoid a large meal for at least 2 hours before the test.
• Avoid smoking for 24 hours beforehand, alcohol for at least 4 hours, and heavy exercise and caffeine for the time your clinic suggests.
• Ask your healthcare team whether you need to pause any inhaler or other medicine. Never stop a medicine without medical guidance ^[1].
• Wear your dentures if you have them, because they help make a tight seal around the mouthpiece ^[1].

5. What happens during spirometry

The test is done by a healthcare professional at a doctor's surgery, clinic or hospital ^[2]. They first check that you are well enough, ask about your health, and measure your height and weight, which are needed to read the results ^[2].

You then sit beside a machine called a spirometer and wear a nose clip. You breathe in fully, seal your lips around a tube and blow out as hard and fast as you can until your lungs feel empty. This is repeated two more times ^[2]. You may be asked to use an inhaler and repeat the test after a short break, to see whether it changes your results ^{[1, 2]}. The whole visit usually takes under an hour ^[2].

6. Understanding the results

Results are compared with typical values for healthy people of the same height, age and sex, because lung size varies ^[1]. A specialist reviews them and sends them to your doctor, and you should get them within a few weeks ^[2].

Abnormal results suggest a lung problem but cannot name the exact disease on their own ^[1]. Doctors often describe two broad patterns ^[1]:

• Obstructive patterns, where the airways are narrowed and it is hard to breathe out. Asthma, bronchitis and emphysema are examples.
• Restrictive patterns, where the lungs cannot hold as much air because they or the chest muscles cannot expand fully. Pulmonary fibrosis and sarcoidosis are examples.

Your doctor explains what your results mean and decides on any next steps, which may include other tests such as a blood test for oxygen and carbon dioxide levels ^[1].

7. Risks and special groups

Risks are very low. You may feel light-headed, dizzy or tired, and coughing is common. Some people feel anxious in the enclosed booth used for lung volume tests ^[1]. The NHS says dizziness or fainting should pass quickly ^[2].

The test is not considered safe in some situations. Tell the clinician beforehand if you have a chest infection, certain heart conditions, uncontrolled high blood pressure, a recent heart attack or stroke, or recent surgery ^[2].

8. When to see a doctor

MedlinePlus lists shortness of breath, wheezing, coughing and a tight feeling in the chest as reasons for a lung function test, so see a doctor if you have them and ask whether a test would help ^[1].

The NHS says it is not safe to have a spirometry test if you have a chest infection, so tell the clinic if you feel unwell before your appointment ^[2].

In an emergency, call your local emergency number (112 in India, 911 in the United States).

9. Conclusion

Lung function tests, and spirometry in particular, are quick and low-risk ways to see how well the lungs are working. They help doctors find the cause of breathing problems and track conditions such as asthma and COPD. Preparing as advised, and telling the clinic about your medicines and health, helps give the most useful result.