Differential cell counts in sputum in respiratory epidemiology: a pilot study

BACKGROUND: The aim of this pilot study was to determine whether measuring sputum differential cell counts, particularly eosinophils, could be a useful method of validating self-reported symptoms suggesting asthma in epidemiologic studies. MATERIALS AND METHODS: In this cross-sectional study, we selected four groups of adult subjects by reported symptoms and diagnoses from among those previously randomly identified in a population study. Subjects were selected with no respiratory symptoms ever (normal group), or reporting a diagnosis of asthma (asthma group), or reporting recurrent wheezing not diagnosed as asthma (wheeze group), or reporting exposure to industrial irritants, but not asthma or wheezing (exposed group). Current respiratory symptoms, airway responsiveness to methacholine challenge, and sputum cell counts were determined. The study was completed by 107 subjects aged 20 to 44 years. RESULTS: There were no significant differences in FEV(1) percent predicted, total cell count, and sputum eosinophil count among the four groups. Subjects with reported asthma had greater airway responsiveness as reflected in a lower bronchial reactivity (BR) index. There was a weak correlation between BR index and sputum eosinophils. CONCLUSION: In a community setting, induced sputum eosinophil cell counts in subjects reporting asthma or wheezing were most often within the normal range and not sufficiently often abnormal to be useful in validating a diagnosis of asthma in epidemiologic studies.