Serial fractional exhaled nitric oxide measurements at and off work may help to identify immunologic occupational asthma in cases with complex exposures.

Serial measurements of fractional exhaled nitric oxide (FeNO) at home and at work have been described to provide complementary information for the diagnosis of occupational asthma (OA) when specific inhalation challenge (SIC) is missing or doubtful. We describe two cases in which serial FeNO measurements enabled the detection of probable OA after complex exposures. A 25-year-old industrial painter with exposure to a variety of paints suffered from work-related airway symptoms for five years. Lung function was normal, and she was not atopic. SIC with hexamethylene diisocyanate was negative. A 47-year-old sign maker (screen printing, foils) suffering from work-related dyspnoea for seven years. Moderate airway obstruction, but no atopy was detectable. Due to the complex exposures SIC was not performed. Both patients performed FeNO measurements once daily during a 2-week-holiday and a subsequent 2-week-work period. In both cases elevated baseline FeNO decreased to normal (25 ppb) during holidays and increased after resuming work (case 1: 125 ppb, case 2: 45 ppb).