IgE and eosinophil count at 6 years old predicts long-term risk of ABPA in children with CF.

<bold>Background:</bold> Allergic bronchopulmonary aspergillosis (ABPA) in people with cystic fibrosis (PwCF) is often diagnosed once lung damage has occurred. CF services around the world screen for ABPA annually. <bold>Aims</bold>: To determine if a diagnosis of ABPA is preceded by changes in total IgE and eosinophil (Eo) levels measured annually. <bold>Methods:</bold> A retrospective analysis of annual data on PwCF 0-18yo in Western Australia from 2000-2020. Total IgE, Asp-RAST and Eo levels were investigated over the time preceding ABPA diagnosis and compared with age- and gender-matched controls. A threshold-based analysis was employed to evaluate the optimal cutoffs for all markers for predicting future ABPA diagnosis. A survival analysis was undertaken to assess the 3 biochemical markers as potential predictors of an impending diagnosis. <bold>Results:</bold> 353 PwCF were identified receiving care over the study period. 342 (96.9%) had annual IgE and Eo data. 17 (4.8%) children developed ABPA, with 14 (4.0%) having data preceding diagnosis. Median (range) age at diagnosis was 11.0yo (5 to 17). Only 1 child developed ABPA <6yo and had rapidly rising IgE levels in the year preceding diagnosis. All ABPA diagnosed ≥6yo were preceded by total IgE, Asp-RAST, and Eo levels above 273 IU/mL, 4.7 IU/mL, and 0.25b cells/L, respectively, in the 6-18 months preceding diagnosis. No child with an IgE level <200 and Eo level < 0.4 from the age of 6yo developed ABPA by 18yo. <bold>Conclusion:</bold> IgE and Eo levels are predictive of ABPA risk in the years preceding diagnosis. PwCF with normal total IgE and Eo levels any time ≥6yo are extremely unlikely to develop ABPA by the age of 18yo, bringing into question the need for annual screening for this group.