Eosinophils

Elevated levels, called eosinophilia, can signal the presence of allergies, asthma, eczema, or parasitic infections, and very high levels may indicate autoimmune conditions or certain blood disorders. Monitoring eosinophil levels can provide early insight into immune system activity and overall inflammatory status.

Most adults benefit from yearly eosinophil percentage testing as part of a CBC differential. When tracking allergic or eosinophilic conditions, retest at 3 to 6 months.

At baseline / for screening: Once every 12 months from age 30 as part of a CBC with differential.

When monitoring an intervention or change: Retest 3 to 6 months when actively tracking allergic, asthmatic, or eosinophilic conditions. After starting or adjusting treatment (inhaled corticosteroids, biologics like dupilumab or mepolizumab, antihistamines), expect 6 to 12 weeks for a meaningful shift. Eosinophil counts have a diurnal rhythm, so standardize timing across draws for reliable trends.

Note: Eosinophils have a diurnal rhythm (higher at night, lower in the morning) and are suppressed by corticosteroids. Standardize draw timing across visits; after stopping steroids, wait 2 to 4 weeks before reading as a stable baseline.