Is bronchial provocation test positivity associated with blood eosinophil count and cut-off value?

Abstract

Asthma is characterized by airway hyperresponsiveness due to chronic inflammation in the airways. One of the main cells involved in airway inflammation is eosinophils. In the current study, a bronchial provocation test (BPT) was performed to demonstrate airway hyperresponsiveness. We investigated the relationship between BPT and blood eosinophil count and the cut-off value of blood eosinophil count. In this study, we retrospectively evaluated the data of 246 patients who visited our immunology and allergy clinic, a tertiary reference center, with asthma symptoms between May 2017 and March 2020 and underwent BPT with methacholine for the diagnosis of asthma. The cases were grouped according to the level of BPT positivity and negativity. Of 246 patients, BPT was positive in 90 (36.6%) and negative in 156 (63.4%). The blood eosinophil measurement of the BPT-positive cases was found to be statistically significantly higher than that of the BPT-negative cases (135 vs. 119 cells/µl, respectively, p=0.029). When BPT is grouped according to positivity levels, there was no statistically significant difference in blood eosinophil measurements between subgroups (p=0.174). As a result of the evaluations, the cut-off point obtained for the blood eosinophil count was determined as ≥226 cells/µl. For the blood eosinophil count, for the cut-off value of ≥226 cells/µl, sensitivity was 30.0%, specificity 87.7%, positive predictive value 58.7%, and negative predictive value 68.3%. This study shows that BPT positivity is associated with blood eosinophil count. The cut-off value (≥226 cells/µl) determined for blood eosinophil count may be helpful when planning BPT and evaluating the diagnosis of asthma.