We do not have very good data to tell us what the most reliable markers of disease activity or predictors of relapse in EGPA are. Eosinophils are one of the subtypes of white blood cells and the level of eosinophils can be measured in the blood. In addition to a careful clinical evaluation, the eosinophil count and other markers of inflammation such as the erythrocyte sedimentation rate (ESR, sed rate) and C-reactive protein (CRP) are usually followed in patients with EGPA. In patients with EGPA who have positive ANCA assays, we also monitor the ANCA level (MPO-ANCA). Some patients with EGPA have elevated IgE levels at the beginning of their disease. In these patients, IgE levels can be useful in follow-up to help predict relapse.
Disease activity is absent in most patients with EGPA when eosinophil levels are low. Prednisone suppresses eosinophil counts quickly and effectively. Therefore, eosinophil counts may drop faster than disease activity disappears. On the other hand, when disease activity recurs, this is usually associated with – or preceded by – increases in eosinophil counts. If increasing eosinophil counts are not addressed by changes in therapy, worsening disease activity often follows.
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