Eosinophil count (EC) as a diagnostic and prognostic marker for infection in the internal medicine department setting

Abstract Introduction . Eosinopenia has been previously investigated as a marker to differentiate infectious from non-infectious diagnoses and as a prognostic marker. Most previous studies were conducted in intensive care unit patients. Our study focuses on the value of eosinopenia in patients admitted to the Internal Medicine department. Methods . We retrospectively analyzed 271 consecutive patients with infection and 31 patients presenting with fever or inflammatory syndrome and a non-infectious diagnosis. We evaluated and compared the following markers for differentiating infectious from non-infectious diagnoses: eosinophil count [EC], CRP, WBC and neutrophil-to-lymphocyte count ratio [NLCR]. We also evaluated the value of eosinopenia as a monitoring parameter in patients with infections. Results . Eosinopenia at admission was found in 71% of patients with infection compared to 32% in the non-infection group. EC and NLCR were moderate markers for discriminating infection from non-infection, with an area under the receiver operating characteristic curve of 0.789 and 0.718 respectively. Significant eosinopenia (≤ 10/µL) had a high specificity (90%) for diagnosing infections. High EC at admission (> 400/µL) was rare in the infection group (1.5%), but not uncommon in the non-infection group (25.8%). Persistent eosinopenia was noted in non-survivors, compared to the rapid normalization of EC in survivors. Conclusions . Among patients presenting with fever and/or high inflammatory markers a low EC is supportive of infection, while a high EC may suggest non-infectious diagnoses. The persistence/ resolution of eosinopenia may be a useful monitoring parameter to predict response to therapy.