PURPOSE: Airway eosinophilia is characteristic of bronchial inflammation in asthma. Blood eosinophil counts are often used as an alternative to sputum eosinophil counts for convenience . Blood eosinophilia is being utilized as a marker for asthma severity and heterogeneity , e.g. to identify likely responders to medications such as mepolizumab, an IL-5 inhibitor. Based on variations observed in our practice, we investigated whether blood eosinophil counts change significantly throughout the day in patients with asthma.
METHODS: We collected serial blood eosinophil counts ( up to eight times within a 12 hour period at intervals of 30 minutes to 5 hours) in two subjects with moderate asthma, two subjects with mild asthma , one subject with allergic rhinitis but no asthma and one control subject with no atopic history.
RESULTS: MB, with moderate asthma, had an initial eosinophil count of 302 with subsequent values ranging from 240 to 490 ( 290,322, 240, 282, 270, 490, 319). TH , with moderate asthma, had an initial eosinophil count of 211, with subsequent values of 78 to 387 ( 211, 146, 387, 148, 114, 252, 78, 164) . SLS, with allergic rhinitis but no asthma, had l counts of 109,76, 92, 67. SS, with mild asthma, had counts of 270,198, 225, 266 . RL , with mild asthma, had counts of 91,101, 91, 99, 86. SSH, with no atopic conditions, had counts of 83, 101, 93, 67.
CONCLUSIONS: These results suggest that eosinophil counts change significantly throughout the day with no obvious allergic triggers or diurnal pattern. These variations were seen in mild and moderate asthma with the widest fluctuations in moderate asthmatics with elevated initial counts. Further research is needed to confirm and investigate the mechanism, significance and factors influencing this surprising observation.
CLINICAL IMPLICATIONS: The use of single blood eosinophil counts for assessment of asthma severity, heterogeneity and in clinical research may need to be reexamined as the values appear to fluctuate throughout the day.
DISCLOSURE: The following authors have nothing to disclose: Sheldon Spector, Ricardo Tan, Amber Malinowski
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