Correlation between Eosinophil Count and Methacholine Challenge Test in Asymptomatic Subjects

Abstract

Background. Methacholine challenge test is used to identify airway hyperresponsiveness (AHR). Total eosinophil counts in peripheral blood reflect asthmatic activity and are useful for early detection of exacerbations. Correlation between the two is poorly defined, particularly in asymptomatic subjects. Objective. The aim is to define correlation between methacholine challenge test and peripheral blood eosinophilia. Methods. All flight academy candidates evaluated in the Israeli Air Force Aero Medical Center between the years 2010 and 2011 were included. Candidates were referred to methacholine challenge test based on a personal history of asthma or wheezing in childhood, a first-degree relative with the diagnosis of asthma, or an abnormal spirometry. All methacholine tests were analyzed retrospectively. Results. Asymptomatic subjects with a positive methacholine challenge test demonstrated significantly (p < .002) higher levels of absolute eosinophil count compared with the group with a negative methacholine test (0.46 ± 0.21 vs. 0.21 ± 0.01 K/μL). Total white blood cell and neutrophil counts were higher in the group with a positive methacholine test compared with the group with a negative methacholine test, but to a lesser extent (7.1 ± 0.25 vs. 6.6 ± 0.09 K/μL, p = .04 and 3.9 ± 0.24 vs. 3.5 ± 0.07 K/μL, p = .04, respectively). No association was demonstrated between eosinophil count and severity of AHR expressed by the methacholine concentration evoking a response. Conclusion. There is a strong association between eosinophil count and AHR in asymptomatic subjects.

• asthma
• diagnosis
• eosinophil
• methacholine

Acknowledgements

No funding was received from any organization. The manuscript was written and the work was performed as a part of the routine activity of the IAF Aero Medical Center, but no financial support was given by any organization, including the IAF or the Israeli Defense Force (IDF).

Nofrat Schwartz and Alon Grossman have contributed equally to this manuscript.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.