# Importance of allergic sensitisation for normal range of fractional exhaled nitric oxide in adolescents

## TL;DR

This study shows that the normal range of exhaled nitric oxide in adolescents depends on their allergic sensitization, suggesting that fixed cutoffs may not be accurate for diagnosing asthma.

## Contribution

The study introduces sensitization-specific FeNO cutoffs for asthma diagnosis in adolescents, challenging fixed clinical thresholds.

## Key findings

- FeNO upper limits vary by allergic sensitization type and sex, with higher values observed in sensitized individuals.
- FeNO above sensitization-specific 95th percentiles is strongly linked to asthma and wheeze in sensitized adolescents.
- Fixed FeNO cutoffs (25 and 50 ppb) poorly represent normal ranges compared to sensitization-specific thresholds.

## Abstract

In addition to body anthropometrics, allergen sensitization has been shown to influence the levels of exhaled fractional nitric oxide (FeNO) in adults, but whether this relationship is valid also in younger age groups, how it compares to the fixed cut‐off levels recommended for clinical practice, and relates to respiratory symptoms remains to be confirmed.

FeNO, sensitization, respiratory symptoms, and spirometry were evaluated in 2054 adolescents taking part in the 16‐year follow‐up of the Swedish BAMSE birth cohort.

The median and upper limit of FeNO was related to the presence and type of allergic sensitisation and poorly represented by one fixed cutoff. For example, the 95th percentiles for sensitisation to dogs were 89 ppb in females and 87 ppb in males. A FeNO value above the sensitisation‐specific 95th percentile was, in those with allergic sensitisation, related to significantly higher odds for current asthma (OR 4.10, 95% CI 2.44–6.89) and wheeze (OR 2.58, 95% CI 1.44–4.62). In those without allergic sensitisation, a FeNO above the 95th percentile was related to wheeze (OR 3.20, 95% CI 1.37–7.51). The odds for having airway obstruction were not related to any of the FeNO cutoffs for either of the groups.

We have shown that the FeNO upper limit of normal is dependent on the presence and type of allergic sensitization and that these cutoffs differ from the fixed cutoffs of 25 and 50 ppb recommended in the literature. Sensitization specific rather than fixed limit cutoffs may be more relevant to asthma diagnosis and asthma symptoms in a general adolescent population.