S120 Causes of negative specific inhalational challenge (SIC) in patients with occupational asthma; the experience of two UK centres

Introduction and objectives Occupational causes are thought to account for 20% of the global burden of asthma. The gold standard test for identifying occupational asthma (OA) is specific inhalational challenge to the suspected occupational agent.1 However, a negative SIC does not always exclude a diagnosis of OA. We investigated the reasons why challenge tests may be negative and associated outcomes from two UK centres. Methods We performed a retrospective review of the outcomes of 79 consecutive negative SICs carried out between 2008 and 2019 in North Manchester General Hospital (NMGH) and Birmingham Heartlands Hospital (BHH). Repeat negative SICs for the same patient were also included. Demographic data, serial peak flow analysis, occupation, current exposures, and progress post SIC were reviewed. Patients were followed up post SIC and further testing (either repeat SIC or other) were performed if ongoing symptoms were present. Results Of the79 negative SICs reviewed, 23 were at NMGH and 56 at BHH. Thirty-six workers (45%) were female, median age 51 years (IQR 41–55.5). Ten workers (13%) had a history of previous asthma. Sixty five percent of SICs had an OASYS score of ≥2.51 i.e. positive for work effect prior to testing. Of the 79 SICs carried out, 50 were subsequently diagnosed with occupational asthma with diagnostic serial PEF records and/or repeat testing. The most common reason for a negative SIC was testing to the wrong agent (figure 1). Conclusions This data suggests that there is a high rate of negative SICs in patients who have a diagnosis of occupational asthma, which is mainly due to exposures to the wrong agent in the SIC. It is crucial that patients are followed up post negative SIC and re investigated early if experiencing ongoing symptoms. Reference Specific inhalation challenge in the diagnosis of occupational asthma: consensus statemen Vandenplas O. et al. European Respiratory Journal 2014 43: 1573–1587.