Eosinophilia is an abnormal increase in the eosinophils (type of white blood cell) in blood or body tissues. Eosinophils are produced in the bone marrow existing normally in the bloodstream and gut lining, which helps the body fight infection from parasitic organisms. On an average around 5% to 7% of white blood cells constitute eosinophils but if you have a higher count then it means that you either have borderline eosinophilia or actual progressing eosinophilia that can cause significant health hazards.
Emphasis is placed on the number of eosinophils circulating in the peripheral blood, although an increase in eosinophils can be observed in other body fluids (eg, cerebrospinal fluid, urine) and many body tissues (eg, skin, lung, heart, liver, intestine, bladder, bone marrow, muscle, nerve).
Eosinophils are derived from hematopoietic stem cells initially committed to the myeloid line and then to the basophil-eosinophil granulocyte lineage. Tissues of the pulmonary and gastrointestinal systems are the normal residence for eosinophils, but peripheral, or blood, eosinophilia (absolute eosinophil count more than 600 per cubic millimeter) indicates an eosinophilic disorder. Eosinophilia can be categorized as mild (less than 1500 eosinophils per cubic millimeter), moderate (1500 to 5000 per cubic millimeter), or severe (more than 5000 per cubic millimeter). An increase in tissue eosinophilia may be seen with or without concurrent peripheral eosinophilia.
In general eosinophilia occurs as a response to parasites (such as filaria or helminths), or from allergy as occurs with asthma and allergic rhinitis, or in some gastrointestinal disorders that may be associated with food allergy. A few drugs or inhaled allergens can cause inflammatory tissue changes accompanied by eosinophilia in susceptible people.
Parasites are a common cause of eosinophilia, and there is often an association with asthma. In occasional patients, an idiopathic hypereosinophilic syndrome occurs, with an eosinophil count in excess of 1500 cells per cubic millimeter of blood, and the heart or nervous system may be affected. Other causes that may be responsible for eosinophilia include collagen-vascular diseases or skin diseases such as pemphigus. Thus, there are numerous rare causes of eosinophilia to consider, although sometimes there is no obvious disease in some people who have prolonged persistence of the high eosinophil count. It is not unusual for the abnormality to eventually clear up without treatment.
Eosinophilia may be primary or secondary. In primary eosinophilia, the increased production of eosinophils is due to an abnormality in a hematopoietic stem cell as, for example, in eosinophilic leukemia. In secondary eosinophilia, the increased production of eosinophils is a reactive process driven by cytokines, as is the case in allergy.