FeNO measurement: how it works.

What the measurement shows.

The FeNO measurement measures nitric oxide in your exhaled breath, a marker of a particular type of airway inflammation that is seen in allergic asthma and can predict the effect of inhaled corticosteroids.

How to prepare.

• No medication pause. Inhaled corticosteroid (preventer) is continued as usual; tell us what you take.
• Avoid eating and drinking, strenuous exercise and smoking/nicotine in the last hour.
• An airway infection within the last 2–4 weeks: please call, and we will assess whether to move the appointment.

Duration

A few minutes.

How it is done.

You empty your lungs, breathe in through the device and then blow out calmly and steadily for about 10 seconds, while a screen helps you keep the pace. This is repeated until two measurements are close to each other. If you are also having spirometry on the same day, FeNO is measured first.

Side effects

None.

Your result

The result is available straight after the measurement.

What to bring

• Bring ID, for example your health insurance card or driving licence (app versions also count) or your passport. Your CPR number alone is no longer enough.
• Bring an up-to-date medication list and any earlier lung function measurements.
• Always bring your reliever inhaler.
• Arrive in good time, so you are not out of breath when we start.

Background and sources

• The clinic's own source for medication pauses and preparation (version 20-10-2026).
• ATS/ERS Recommendations for Standardized Procedures for the Online and Offline Measurement of Exhaled Lower Respiratory Nitric Oxide and Nasal Nitric Oxide. Am J Respir Crit Care Med 2005;171:912–930.
• Dweik RA et al. An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications. Am J Respir Crit Care Med 2011;184:602–615.

Lung function test