Eosinophils respond to parasite infections, play a role in hypersensitivity reactions (allergic reactions) and control the intensity of the immune response and inflammation. The analysis provides both the number of eosinophils per litre of blood (eosinophil #) or the fraction of total leukocytes they represent (eosinophil ratio). Results must be interpreted in light of clinical observations, other results from the current blood count, and variations in results over time.
A high number and/or ratio of eosinophils are found in asthma and allergic reactions of all types (rhinitis, sinusitis, hives, eczema, and antibiotic, antifungal and psychotropic medications, etc.), in inflammatory diseases (celiac disease or gluten-sensitive enteropathy, Crohn’s disease, etc.) or in helminth parasitic infections (round intestinal worms) and some malignant diseases.
Given the difficulty in measuring a small number of eosinophilic leukocytes, a lower number or ratio of eosinophils (eosinophilia) is generally of little clinical significance.