Eosinophilia detected by automated blood cell counting in ambulatory North American outpatients. Incidence and clinical significance.

OBJECTIVES

To audit a cohort of ambulatory outpatients with eosinophilia detected on automated blood cell counting. Specific objectives included the determination of whether the eosinophilia had been anticipated, the etiology of the eosinophilia, the clinical follow-up and investigations performed on patients with eosinophilia, and the effect of the detection of eosinophilia on patient management and ultimate clinical outcome.

DESIGN

A year-long retrospective review of all patients with an absolute eosinophil count of greater than 0.7 x 10(9)/L.

SETTING

A large outpatient laboratory system. The patient population was managed by family physicians and specialists.

INTERVENTION

Data collection included the results of the hematology profile, the absolute eosinophil count, the clinical situation responsible for the hematologic profile determination, and the probable cause of eosinophilia. Individual physicians were surveyed to determine if discovery of the eosinophilia had changed patient management plan or clinical outcome.

PRINCIPAL RESULTS

Out of 195,300 patients who had a hematology profile performed, 225 were found to have an absolute eosinophilia count higher than 0.7 x 10(9)/L. The overall incidence of eosinophilia in the study population was 0.1%. The eosinophilia was not anticipated in 85% of patients. No obvious cause was detected for the eosinophilia in 36% of patients. Various allergic diseases were responsible for the eosinophilia in the majority of the remaining patients. Fewer than 9% of individuals manifested a serious systemic illness or parasitemia. Further clinical follow-up had been performed in 69% of patients. Additional laboratory tests had been ordered in 59% of patients. The laboratory tests most frequently ordered were a repeat hematology profile or stool examinations for ova and parasites. In only two instances did the discovery of the eosinophilia appear to result in a significant change in patient management or ultimate clinical income.

CONCLUSION

The vast majority of eosinophilias detected in ambulatory outpatients are associated with allergic processes. An extensive investigation of eosinophilia in ambulatory North American outpatients does not appear to be warranted unless specifically indicated by the results of the history and physical examination.