FeNO Breath Analysis

FeNO stands for fractional exhaled nitric oxide. It is a quick, painless breath test that measures a marker of a particular type of airway inflammation. A raised level supports an asthma diagnosis and predicts a good response to inhaled steroid treatment. At Allergy Asthma Foundation it is carried out by an experienced team using current equipment and protocols, with clear information given before, during and after so that you know what to expect at every stage.

This page explains why the procedure is done, how to prepare, what happens on the day, and what recovery and follow-up involve. Your own consultant will go through the details that apply to your situation and answer any questions before you agree to go ahead.

Why it is done

FeNO breath analysis is usually recommended for one or more of the following reasons:

• Helping to confirm or rule out asthma when the diagnosis is uncertain
• Judging whether inhaled steroid treatment is likely to help
• Checking whether a preventer inhaler is being taken and is working
• Investigating a chronic cough
• Monitoring airway inflammation over time

It is only offered when the expected benefit clearly outweighs the risks, and the decision is always made together with you. If a simpler test or treatment would answer the question or relieve the problem, that is tried first.

How to prepare

• Bring a list of your current medicines and any earlier results for the same test.
• Ask the team whether any medicine needs to be paused beforehand — for some tests, antihistamines or inhalers are held for a short, specified time.
• Wear comfortable, loose clothing.
• Avoid a heavy meal, vigorous exercise and strong coffee in the hour before the test.
• Allow a little extra time; the appointment includes explanation and practice, not only the measurement itself.

What happens on the day

1. You sit comfortably and take a full breath in through the mouthpiece.
2. You then breathe out slowly and steadily at a fixed, gentle rate, guided by an animation or a gauge.
3. The device analyses the breath and shows a number within a minute.
4. The measurement is usually repeated to check it is consistent.
5. No nose clip is needed and there is nothing to inhale.

After the procedure

There is nothing to recover from. Avoid a heavy meal, vigorous exercise and, if it is safe to do so, short-acting inhalers in the hour before the test, as these can affect the reading.

You will be given written instructions covering activity, wound or puncture-site care where relevant, which medicines to restart and when, and the warning signs that mean you should contact us or attend the emergency department. A follow-up appointment or a phone review is arranged before you leave.

Benefits and risks

The main benefit is a clear answer or effective treatment that changes what happens next — a firm diagnosis, a blocked passage reopened, symptoms brought under control, or a condition safely monitored over time. For most people the procedure is straightforward and complications are uncommon.

No procedure is entirely without risk. The ones to be aware of for this treatment include:

• No known risk from the test itself
• The reading can be affected by recent food, exercise, smoking or a cold, so context matters
• A normal result does not completely exclude asthma, and the number is read alongside symptoms and other tests

The team is trained and equipped to recognise and manage these, and the consent discussion covers how likely each is in your case and what is done to reduce it.

Results and follow-up

The result is available immediately and your clinician will explain what it means for your diagnosis or your inhaler treatment at the same visit. Your consultant explains what the result means in the context of your symptoms and examination, and sets out the next step — reassurance and discharge, a change of treatment, a further test, or a planned review. With your consent a summary is sent to your family doctor so that everyone caring for you is working from the same plan.

Questions patients ask

Do I need a referral?

You can book a consultation directly to discuss whether feno breath analysis is right for you. The procedure itself is arranged by the consultant after that discussion, once you have had time to consider it.

Will it hurt?

Discomfort is kept to a minimum with local anaesthetic, sedation or pain relief as appropriate to the procedure. The team will tell you exactly what you are likely to feel and will stop or pause if you need them to.

How long will I be at the hospital?

Most people are in and out within a few hours; where an overnight stay or a longer recovery is expected, that is explained clearly when the procedure is booked so you can plan around it.

To arrange feno breath analysis at your nearest AAF centre, book a consultation online or request a callback. Please bring a list of your current medicines and any previous test results or discharge summaries.