The present disclosure relates to the use of protein and/or gene expression levels of dipeptidyl peptidase-4 (DPP4/CD26) and periostin (POSTN) as peripheral biomarkers for eosinophilic diseases or disorders, e.g., moderate to severe asthma. Levels of the DPP4 and/or POSTN above or below predetermined DPP4 or POSTN threshold levels can be used, e.g., (i) to determine a patient's eligibility for a certain treatment with an IL-5R antagonist, e.g., an anti-IL- 5R antibody such as benralizumab (MEDI-563), (ii) to determine whether a certain treatment of an eosinophilic disease or disorder with a specific IL-5R antagonist should commence, be suspended, or be modified, (iii) to diagnose whether an eosinophilic disease or disorder is treatable or not treatable with a specific IL-5R antagonist, (iv) to prognosticate the outcome of treating an eosinophilic disease or disorder with a specific IL-5R antagonist, etc.
