Exhaled nitric oxide (FeNO) greater than 42 ppb discriminates between eosinophilic and non-eosinophilic asthma

It has been claimed that exhaled nitric oxide (FeNO) could be regarded as a surrogate marker for sputum eosinophil count in patients with asthma. However, the FeNO threshold value that identifies a sputum eosinophil count ≥3% in patients with asthma has been poorly studied.

This retrospective study included 295 patients with asthma aged 15–84 years.

FeNO ≥41 ppb gave 65% sensitivity and 79% specificity for identifying a sputum eosinophil count ≥3%.

A threshold of 42 ppb was found to discriminate between eosinophilic and non-eosinophilic asthma.

Patients receiving high doses of ICS (≥1000 μg beclometasone) had a significantly lower FeNO threshold (27 ppb) than the rest of the group (48 ppb).

Atopy also significantly altered the threshold (49 ppb for atopic vs 30 ppb for non-atopic patients) and there was a trend for a lower threshold in smokers (27 ppb) compared with non-smokers (46 ppb).

High-dose ICS and smoking were independent predictors of sputum eosinophilia.

FeNO is able to identify a sputum eosinophil count ≥3%. Thresholds vary according to dose of ICS, smoking and atopy.

Inflammation in asthma (mind map). FeNO is a marker of oxidative stress. See more Allergy and Immunology mind maps here.

NIOX MINO display. The device needs to be plugged in at all times.

However, a 2012 study in the journal Thorax, showed that tailoring of asthma treatment based on FeNO levels was ineffective in improving outcomes in children and adults.

Exhaled nitric oxide thresholds associated with a sputum eosinophil count ≥3% in a cohort of unselected patients with asthma. Thorax 2010;65:1039-1044 doi:10.1136/thx.2009.124925
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