Background and objective: The use of fractional exhaled nitric oxide (FeNO) concentration has been proposed as a surrogate marker for monitoring airway response to specific inhalation challenge (SIC). We investigated the usefulness of FeNO measurements for monitoring airway response to SIC with occupational agents.

Material and methods: Workers with suspected occupational asthma were recruited to undergo SIC with occupational agents and subsequently FeNO testing at baseline and 24 hours.

Results: Sixty-eight patients were evaluated, 45 of whom had a positive SIC. SIC-positive patients showed a significant increase in FeNO 24 hours postchallenge, with an increase ratio of 1.25 (95% CI, 1.05-1.48; P=.01); no increase was seen in patients with a negative SIC (P=.08). The predictive capacity of variations in FeNO showed that for each unit increase in FeNO, the probability of a positive SIC rose by 4%. A baseline FeNO value of 25 ppb predicted a positive SIC with 60% sensitivity and 80% specificity. The increase in %FeNO cutoff point providing maximal sensitivity and specificity for predicting a positive SIC was 41% (sensitivity 50%, specificity 95%).

Conclusions: We demonstrated that asthmatic reactions induced by occupational agents during SICs are associated with a consistent increase in FeNO. However, the predictive diagnostic capacity of FeNO measurements is low. While FeNO may aid in the interpretation of SIC in some cases, it cannot be used as a general surrogate marker to predict or to assess SICs with occupational agents.

Key words: Occupational asthma. Fractional exhaled nitric oxide. Specific inhalation challenge. Bronchial inflammatory markers.