Specific Inhalation Challenge in Persulfate Asthma

Specific inhalation challenge (SIC) may be considered the 'gold standard' for the diagnosis of occupational asthma due to persulfate salts. The aim of the study was to develop a safe SIC protocol. Between 2003 and 2014, eight patients with suspected occupational asthma due to persulfate salts were examined (7 females, all hair-dressers). SIC was done with a dosimeter and a nebulizer using ammonium persulfate dissolved in phosphate buffer. Until 2009, a four-step-protocol (doses: 0.0004, 0.0045, 0.045, 0.45 mg; cumulative: 0.5 mg) was used, afterwards a six-step-protocol (doses: 0.0004, 0.0018, 0.007, 0.028, 0.113, 0.45 mg; cumulative: 0.6 mg). With each SIC protocol, four subjects were tested. Skin prick tests with ammonium persulfate (20 mg/mL) were performed in all and patch tests in four subjects. In total, four subjects showed a positive SIC, two with each protocol. All subjects showed an isolated late reaction. The greatest decrease of volume in 1 s was 35 % about 3.5 h after the last inhalation (four-step-protocol). Skin prick test with ammonium persulfate was positive in one SIC positive (2 mm wheal) and in two SIC negative patients (3 and 4 mm wheal). All four subjects tested with patch tests showed a positive reaction; three of them were SICpos. We recommend to include patch-testing in the diagnosis of suspected occupational asthma due to persulfate salts. Isolated late asthmatic reactions may occur after SIC. The proposed six-step SIC protocol was safe in this limited number of subjects.