Optimizing diagnostic tests for persulphate-induced respiratory diseases
SIC
In this study, we aimed at improving the currently validated SIC with persulphate. The improvements consisted of: a more rapid approach; using the “stirring method” instead of the “tipping method”; and assessing not only asthma but also rhinitis.
When Munoz et al. validated the realistic method [20], repeated exposures on consecutive days were performed with a mixture of potassium persulphate and 150 g lactose using the tipping method. The duration of the exposure was 10 min each day, and the dose of potassium persulphate was increased from 5 to 30 g over 4 days until a positive reaction occurred. The patient was hospitalized during the entire procedure. The method proved safe and a sensitivity of 100 % and a specificity of 87.5 % for diagnosing occupational asthma were reported.
In our method, we skipped the first 3 days with low exposure, and went straight to exposing the patient to 30 g of potassium persulphate. Instead of 10 min exposure we performed 15 min exposure. To reduce the risk of adverse reaction, exposure was performed step-wise; 5 min at a time with 20 min pauses in between, and severe asthmatic reactions and/or anaphylactic reactions to bleaching products were considered exclusion criteria.
Given that none of the symptomatic controls with allergic asthma and rhinitis reacted to SIC, it seems that the proposed method has a high specificity for persulphate-induced asthma and rhinitis. In this group of hairdressers, SIC produced a nasal response in 33 % (6/18 with work-related rhinitis symptoms) and a bronchial response in 11 % (2/18 with work-related asthma symptoms).
We registered no adverse events or severe asthmatic reactions although our exposure was higher than Munoz’ on the fourth day. Hence, it seems that the rapid method is safe when tested in patients without a history of severe asthmatic reactions or anaphylactic reactions to bleaching products.
We have several reasons for using the level of exposure we did. Firstly, we chose 3 × 5 min exposure to better mimic the hairdressers’ exposure during a typical working day. Since hairdressers are mainly exposed to persulphates when they mix bleaching powder with hydrogen peroxide [32], we wanted to mimic this process. We estimated that a typical hairdressers performs this process three times a day. Secondly, the ratio of persulphate to lactose powder was changed as to better mimic the level hairdressers are exposed to in their daily practice. During mixing of the paste that is applied to the clients hair, 20–80 g bleaching powder [33], containing up to 60 % persulphate (12–48 g) [1], is typically used. We therefore used a ratio of persulphate to lactose powder of 3:2 (30 g persulphate:20 g lactose powder). To obtain a more uniform and reproducible exposure, we used a magnetic stirrer. In our study, the participants were exposed to levels of up to 0.34 mg/m3 for 3 × 5 min during SIC. The permissible threshold limit value of exposure to potassium persulphate, as defined by the Occupational Safety and Health Administration in the United States, is a time weighted average (TWA) of 0.1 mg/m3 during a typical working day of 8 h. According to the excursion limit of potassium persulphate, the TWA should not be exceeded more than 3 times for no longer than 30 min during a working day. Hence, the TWA was exceeded during our exposure, but the excursion limit was respected.
A limitation of our approach is that the patients were sent home after 8 h of observation in the clinic. This is convenient for the patient, but it introduces a potential bias. If the patient develops a positive nasal or bronchial response during this period at home, it is difficult to interpret whether the response was caused by exposure to persulphates or by exposure to other allergens encountered outside the hospital. However, in our study, all hairdressers reacted whilst being monitored in our department, so it is unlikely that this is a problem in our results.
Another limitation of our study is that the included hairdressers were merely under suspicion of having occupational asthma and rhinitis, but they were not clear-cut cases, which explains why only some hairdressers had a positive reaction to SIC. Firstly, they did not have serial peak flow measurement at and away from work performed prior to inclusion. If we had included only patient with a peak flow pattern suggestive of occupational asthma it might have improved the sensitivity of the test for detecting persulphate-induced asthma. Secondly, many had normal findings in spirometry, FeNO, and the methacholine challenge suggesting that they did not in fact have asthma although they reported asthmatic symptoms. Third, although persulphates are considered the major cause of occupational asthma and rhinitis in hairdressers [34] more than half reported that their work-related respiratory symptoms could also be provoked by other hairdressing products suggesting that their respiratory symptoms were not merely caused by persulphates. Also, some of the hairdressers had not been active hairdressers for several years and therefore were not still exposed to persulphates meaning that they could have lost airway responsiveness. Taken together, several factors exist that could explain why not all hairdressers reacted to the SIC and consequently the sensitivity of our approach cannot be determined.