Diagnosis of Hypereosinophilic Syndrome Exclusion of secondary eosinophilia Tests to identify organ damage Bone marrow examination with cytogenetic testing if secondary causes of eosinophilia are not identified Evaluation for hypereosinophilic syndrome should be considered in patients who have peripheral blood eosinophilia > 1500 / mcL (> 1.5 × 10 9 / L) present on more than one occasion that is unexplained, particularly when there are manifestations of organ damage.