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.
References:
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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