Incidence and Clinical Significance of Unsuspected Eosinophilia Discovered by Automated WBC Differential Counting

We analyzed 38,086 ambulatory outpatients and found that 60 individuals bad absolute eosinophilia associated with an otherwise normal hematologic profile. In 43 patients, the eosinophilia was not anticipated. No obvious cause was detected for the unanticipated eosinophilia in 50% of the patients. Allergic diseases were responsible for the eosinophilia in the majority of the remaining patients, with fewer than 10% of these patients manifesting a serious systemic illness or parasitemia. Additional laboratory tests were ordered for 25 patients; the tests most often ordered were repeat hematologic profiles or stool examinations for ova and parasites. We found the concurrent occurrence of eosinophilia with a normal hematologic profile unusual (incidence <0.2% of cases).