Eosinophils are a normal cellular component of the blood and also of certain tissues, including spleen, lymph nodes, thymus, and the submucosal areas of the gastrointestinal, respiratory, and genitourinary tracts. Counts of 0 to 450 eosinophils per cubic millimeter of blood are considered within normal limits. Eosinophilic disorders occur when eosinophils are found in above-normal amounts in various parts of the body.
When the body wants to attack a substance, such as an allergy-triggering food or airborne allergen, eosinophils respond by moving into the area and releasing a variety of toxins. However, when the body produces too many eosinophils, they can cause chronic inflammation resulting in tissue damage. Eosinophilic disorders are diagnosed according to the location where the levels of eosinophils are elevated:
There are many disorders where eosinophils have been found elevated in the blood or in different tissues. General categories of disease that have increased levels of eosinophils range from allergic disorders to endocrine disorders.