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

Area of Science:

• Pulmonary Medicine
• Epidemiology
• Allergy and Immunology

Background:

• Validating self-reported asthma symptoms in epidemiological studies is crucial.
• Sputum differential cell counts, specifically eosinophils, were investigated as a potential biomarker.
• Previous methods for symptom validation in large populations have limitations.

Purpose of the Study:

• To assess the utility of sputum eosinophil counts in validating self-reported asthma symptoms within an epidemiological context.
• To determine if elevated sputum eosinophils correlate with asthma diagnosis or recurrent wheezing.
• To evaluate the feasibility of using sputum analysis in community-based epidemiological research.

Main Methods:

• A cross-sectional study involving 107 adult subjects aged 20-44 years.
• Four groups were selected: normal, diagnosed asthma, recurrent wheezing, and industrial irritant exposure.
• Measurements included respiratory symptoms, methacholine challenge for airway responsiveness, and sputum differential cell counts.

Main Results:

• No significant differences in FEV1 percent predicted, total sputum cell count, or sputum eosinophil count were observed across the four groups.
• Subjects with a reported asthma diagnosis exhibited greater airway responsiveness (lower bronchial reactivity index).
• A weak correlation was found between the bronchial reactivity index and sputum eosinophil levels.

Conclusions:

• Induced sputum eosinophil counts in subjects reporting asthma or wheezing were predominantly within the normal range.
• Abnormal sputum eosinophil counts were not frequent enough to reliably validate asthma diagnoses in epidemiological studies.
• Sputum eosinophil counts are unlikely to be a practical tool for validating asthma in community-based epidemiologic research.