Correlation between eosinophil count and methacholine challenge test in asymptomatic subjects.

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. The aim is to define correlation between methacholine challenge test and peripheral blood eosinophilia. 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. 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. There is a strong association between eosinophil count and AHR in asymptomatic subjects.