Spirometry Test: What It Shows, How It Works and What Results Mean

A spirometry test is a breathing test that measures how much air you can blow out and how quickly you can do it. It helps a clinician investigate symptoms such as persistent cough, wheezing and breathlessness. It is also used when assessing conditions including chronic obstructive pulmonary disease (COPD) and asthma, or monitoring an existing lung condition.

If you have been told you need spirometry, you may want to know what the test feels like and what the numbers mean. The test itself is straightforward, but the result needs to be interpreted alongside your symptoms, medical history and sometimes other investigations. The NHS describes spirometry as a lung function test; it is one part of an assessment rather than an answer to every breathing problem.

What does a spirometry test measure?

You breathe out through a mouthpiece attached to a spirometer after filling your lungs. The device records the amount of air exhaled and how quickly it comes out. The main measurements you might see on a report are:

• FEV1: the amount of air you can force out in the first second of a breath.
• FVC: the total amount of air you can force out after taking a full breath in.
• FEV1/FVC ratio: the proportion of your total exhaled air that comes out in the first second. A reduced ratio suggests airflow obstruction.

Results are compared with reference values relevant to the individual. A clinician also checks whether the blows were technically acceptable and consistent enough to interpret. One isolated number is rarely the whole story.

There is no single “normal spirometry value” for everyone. A report should be considered in the context of the person's age, height and other relevant factors, the laboratory's reference method and the quality of the test.

Why might you need a spirometry test?

Your clinician may recommend spirometry if you have:

• Shortness of breath, particularly if it is new or persistent
• Wheezing or chest tightness
• A cough that does not settle
• Breathlessness during activities that used to feel manageable
• A known lung condition that needs review

Spirometry may help investigate asthma or COPD and can help monitor how lung function changes. It may also be requested before some operations, or as part of workplace health surveillance such as asbestos medicals and some occupational health assessments.  A pattern that suggests restriction can prompt further assessment, but spirometry does not diagnose pulmonary fibrosis on its own.

How is spirometry used to diagnose COPD?

For someone with symptoms and relevant risk factors, spirometry helps show whether airflow obstruction remains after an inhaled bronchodilator, a medicine that opens the airways. The test is done before and again after the medicine where appropriate.In adults, a post-bronchodilator FEV1/FVC ratio below 0.7 supports persistent airflow obstruction in the right clinical context. You can't diagnose COPD from a screenshot or a home reading. NICE also cautions that a fixed threshold needs careful interpretation in older and younger people; symptoms, exposure history, test quality and other possible causes matter.

Is spirometry accurate for COPD?

Good-quality post-bronchodilator spirometry is central to confirming airflow obstruction, but accuracy depends on a well-performed test and appropriate interpretation. A low ratio does not by itself explain every symptom or establish the full severity of someone's illness. Conversely, a result that does not show obstruction may lead the clinician to look for other causes of breathlessness or to review whether repeat testing is needed.

Spirometry may also be used while monitoring COPD, but treatment decisions are based on more than repeated numbers. Your symptoms, exacerbations and daily functioning also matter.

Can spirometry help diagnose asthma?

Yes. Spirometry can show airflow obstruction, and bronchodilator reversibility testing checks whether lung function changes after an inhaler. That change may support an asthma diagnosis. However, asthma symptoms can vary, so normal spirometry on one day does not automatically rule it out.

The current BTS/NICE/SIGN asthma guideline uses a sequence of objective tests for diagnosis; depending on the situation, this may include FeNO, blood eosinophils, bronchodilator reversibility, peak-flow monitoring or specialist testing. A clinician chooses the appropriate asthma testing pathway rather than relying on spirometry alone to distinguish asthma from COPD.

What happens during a spirometry test?

A healthcare professional first checks whether the test is suitable for you and explains how to perform it. You will usually sit down, wear a soft nose clip, seal your lips around a clean mouthpiece, take a deep breath and blow out as hard and fast as you can until your lungs feel empty. The test is repeated so the practitioner can check that the measurements are reliable. NHS spirometry guidance

The original article describes three approaches. They fit together as follows:

How should you prepare?

Follow the instructions from the testing service. You may be asked to avoid smoking, alcohol, a large meal or strenuous activity beforehand, and to wear clothing that does not restrict breathing. You may also receive specific instructions about inhalers. Do not stop prescribed inhalers or other medicines unless your clinician or testing service tells you to. The NHS preparation guide explains the usual steps.

Tell the service if you have a current chest infection, have recently had a heart attack, stroke or surgery, have uncontrolled blood pressure, or have another condition that might make forced breathing unsuitable. The practitioner may postpone the test or seek advice. Spirometry is generally well tolerated, although the repeated effort can make some people briefly lightheaded or tired. Stop and tell the practitioner if you feel unwell.

What do spirometry test results mean?

After testing, the clinician reviews whether the results were repeatable and explains them in the context of your symptoms. A report might describe obstruction, possible restriction or measurements within the expected range. None of those phrases should be used to diagnose yourself from a single result.

If a test suggests COPD, the clinician considers the post-bronchodilator ratio and the wider history. If asthma remains possible despite a normal result, further tests or repeat assessment may be advised. A reduced FVC may lead to additional tests of lung volumes, sometimes through a specialist referral, rather than an immediate diagnosis. Ask when you will receive the interpreted report and whom to contact if you have questions.

How much is a private spirometry test?

A private spirometry test is listed at £195 on Private Medical Clinic's published on fees page. Before booking, confirm the current price, which clinics perform the test, whether bronchodilator reversibility and a written interpretation are included, and whether a separate GP consultation is needed. Availability and the exact testing package should not be assumed from the fee listing alone.

If you have an ongoing cough or breathlessness and are unsure which investigation you need, a private GP consultation can help assess your symptoms and discuss whether spirometry or another next step is appropriate. A online gp consultation can discuss symptoms but cannot carry out the breathing test remotely.

Next steps

If a cough, wheeze or breathlessness keeps returning, discuss it with a clinician rather than trying to interpret a home reading or a single report. They can explain whether spirometry is appropriate, what the result shows and whether any further tests or treatment are needed. If you are considering private testing, check the current spirometry fee and ask the clinic to confirm availability and what the appointment includes.

Frequently asked questions