A practical workup for eosinophilia. You can investigate the most likely causes right in your office

The vast majority of cases of eosinophilia in North America are caused by allergic processes. In individual cases, a short differential diagnosis of the most likely causes can be formulated on the basis of the absolute eosinophil count. The extensive laboratory workup previously recommended by some authorities is probably not justified unless detailed history taking and physical examination indicate a need for specific investigations. Although the possibility of missing an occult neoplasm has been used to justify extensive investigation, this is usually not necessary because most tumor-associated eosinophilia is accompanied by widely metastatic disease. History taking should emphasize the possibility of drug-induced or helminth-associated eosinophilia. If the history indicates travel, dietary, or other exposure risks, stool examination for ova and parasites is worthwhile. If a possible allergic cause is suspected, testing for evidence of atopy may be performed concomitantly with testing for parasitic infection. A follow-up white blood cell count with differential is recommended to ascertain whether eosinophilia has resolved. When an absolute eosinophil count of more than 1.5 x 10(9)/L persists for longer than 6 months, idiopathic hypereosinophilic syndrome must be ruled out.