What is an exhaled carbon monoxide test?
An exhaled carbon monoxide test measures how much carbon monoxide is in your body.
It’s simple and easy to do. You do not need to prepare for the test.
What is carbon monoxide?
Carbon monoxide (CO) is a poisonous gas that you cannot see, smell or taste.
Carbon monoxide is found in:
- cigarette smoke
- exhaust fumes
- broken gas appliances, like boilers.
Carbon monoxide is harmful because it limits the amount of oxygen that is carried round your body.
What’s an exhaled carbon monoxide test used for?
The exhaled carbon monoxide test is a useful tool to monitor how much carbon dioxide is in your body. Most people with high levels of carbon monoxide smoke.
Exhaled carbon monoxide tests are usually offered to:
- people who smoke
- pregnant women.
The test can show you what harm smoking is causing. It can be a useful tool to help you quit, with other smoking cessation support. You can use the test to measure your progress after you stop smoking.
The test can also show if you’re being exposed to dangerous levels of carbon monoxide in second-hand smoke, even if you don’t smoke yourself.
Being exposed to carbon monoxide if you’re pregnant is a risk to your baby because it affects how much oxygen they get. Your baby needs oxygen to grow and develop. Read more about how passive smoking affects children’s lungs.
What happens during an exhaled carbon monoxide test?
You will be asked to hold your breath for as long as possible, ideally 15 seconds. Then you will breathe out slowly into a tube attached to a hand-held monitor, trying to empty your lungs completely.
The monitor shows you the reading within 30 seconds.
What do my results mean?
The results will show how many parts per million (ppm) of carbon monoxide is in your breath. Your healthcare professional will help you to understand your result.
| Reading on the screen | This means that: |
|---|---|
| 10ppm and over | you have recently been exposed to a high level of carbon monoxide. This is common if you smoke. |
| 5-9ppm | you have recently been exposed to a mild level of carbon monoxide. This may mean that you smoke, or you’ve been exposed to second-hand smoke. |
| 1-4ppm | you have recently been exposed to a low level of carbon monoxide. It’s normal to have a small amount of CO in your breath, even if you do not smoke. |
Help to stop smoking
Stopping smoking is not always easy, but there’s lots of help and support available. Check out our information and resources on how to stop smoking.
Contact the National Gas Emergency service on 0800 111 999 if:
Your reading shows a high level of carbon monoxide, but you do not smoke. It’s possible that you have a faulty appliance in your home.
Get support
Call or email our helpline for support with your condition. Get advice on medicines, symptoms or travelling with a lung condition. You can also find support through our groups.
