Serial measurements of exhaled nitric oxide at work and at home: a new tool for the diagnosis of occupational asthma.

Whereas serial measurements of lung function at work and at home are a well-known diagnostic tool for the diagnosis of occupational asthma (OA), little is known about the serial measurements of non-invasive parameters such as exhaled nitric oxide (eNO). A 51-year-old baker with variable shortness of breath without relation to work was examined for suspected OA. Skin prick test showed weak sensitizations to wheat and rye flour (without sensitizations to environmental allergens) that were corroborated by in vitro testing (CAP class 3). Baseline FEV1 of 58% predicted and a decrease of forced expiratory volume in 1 s (FEV1) after placebo (sugar powder) of 17% did not allow inhalational challenge testing. The patient performed daily measurements of FEV1 and eNO for about a month during a holiday at home and at work. Whereas symptoms and FEV1 did not show differences between holidays and work periods, eNO showed a clear increase from below 10 ppb to a maximum of 75 ppb. A diagnosis of baker's asthma was made, and the patient quit his job immediately after medical advice. A year afterwards, the patient was still taking asthma medication, but his symptoms had improved, FEV1 had increased to 73% predicted, and eNO was 25 ppb. We conclude that serial measurements of eNO at home and at work may be a useful tool for the diagnosis of OA.