The doctor is likely to have to administer many tests to look for one of the conditions that could cause the eosinophil count to increase.  These tests will probably include blood tests, X-rays or scans such as ultrasounds and CT scans, stool samples to look for infections and tests on the heart.  Sometimes a bone marrow biopsy will also be needed. In a fraction of patients with HE or CEL a change in a two proteins are rearranged and stuck together making a protein called FIP1PDGFR. This can be tested for in blood or bone marrow. It is important to look for this as special drugs are used for patients with this genetic change.