Eosinophils are a type of white blood cell Overview of White Blood Cell Disorders White blood cells (leukocytes) are an important part of the body’s defense against infectious organisms and foreign substances (the immune system). To defend the body adequately, a sufficient... read more that play an important role in the body's response to allergic reactions Overview of Allergic Reactions Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies make people sneeze; the eyes water and itch... read more , asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more , and infection with parasites Overview of Parasitic Infections A parasite is an organism that lives on or inside another organism (the host) and benefits (for example, by getting nutrients) from the host at the host's expense. Although this definition actually... read more . These cells have a role in the protective immunity against certain parasites but also contribute to the inflammation that occurs in allergic disorders.
Sometimes, eosinophils cause inflammation in certain organs that results in symptoms.
Eosinophils usually account for less than 7% of the circulating white blood cells (100 to 500 eosinophils per microliter of blood [0.1 to 0.5 × 109 per liter]).
Low number of eosinophils
A low number of eosinophils in the blood (eosinopenia) can occur with Cushing syndrome Cushing Syndrome In Cushing syndrome, the level of corticosteroids is excessive, usually due to taking corticosteroid drugs or overproduction by the adrenal glands. Cushing syndrome usually results from taking... read more , bloodstream infections (sepsis Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more ), and treatment with corticosteroids. However, a low number of eosinophils does not usually cause problems because other parts of the immune system compensate adequately.
A low number of eosinophils is usually detected by chance when a complete blood count is done for other reasons.
Treatment of the cause restores the normal number of eosinophils.
High number of eosinophils
The most common causes of a high number of eosinophils (called eosinophilia or hypereosinophilia) are
Infections by parasites
Allergic disorders, including drug sensitivities Drug Rashes Drug rashes are a side effect of a drug that manifests as a skin reaction. Drug rashes usually are caused by an allergic reaction to a drug. Typical symptoms include redness, bumps, blisters... read more , asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more , allergic rhinitis Allergic Rhinitis Rhinitis is inflammation and swelling of the mucous membrane of the nose, characterized by a runny nose and stuffiness and usually caused by the common cold or a seasonal allergy. Colds and... read more , and atopic dermatitis Atopic Dermatitis (Eczema) Atopic dermatitis (commonly referred to as eczema) is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who... read more , often increase the number of eosinophils. Many parasites Overview of Parasitic Infections A parasite is an organism that lives on or inside another organism (the host) and benefits (for example, by getting nutrients) from the host at the host's expense. Although this definition actually... read more , particularly ones that invade tissue, cause eosinophilia. Cancers that cause eosinophilia include Hodgkin lymphoma Hodgkin Lymphoma Hodgkin lymphoma is a type of lymphoma distinguished by the presence of a particular kind of cancer cell called a Reed-Sternberg cell. The cause is unknown. Lymph nodes enlarge but are usually... read more , leukemia Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more , and certain myeloproliferative neoplasms Overview of Myeloproliferative Neoplasms In myeloproliferative neoplasms (myelo = bone marrow; proliferative = rapid multiplication; and neoplasm = new abnormal growth), the blood-producing cells in the bone marrow (precursor cells... read more .
If the number of eosinophils is only slightly elevated, people usually do not have symptoms, and the high number of eosinophils in the blood is only discovered when a complete blood count is done for other reasons. However, sometimes, particularly when the number of eosinophils is very high, the increased number of eosinophils inflames tissues and causes organ damage. The heart, lungs, skin, and nervous system are most often affected, but any organ can be damaged.
Symptoms are related to the organ affected. For example, people may have a rash when the skin is affected, wheezing and shortness of breath when the lungs are affected, shortness of breath and fatigue (symptoms of heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more ) when the heart is affected, or throat and stomach pain when the esophagus or stomach is affected. Accordingly, eosinophilic disorders are diagnosed according to the location where the levels of eosinophils are elevated:
Eosinophilic cardiomyopathy (heart)
Eosinophilic colitis (large intestine)
Eosinophilic enteritis (small intestine)
Eosinophilic gastritis (stomach)
Often, people are first tested and treated for more common causes of their symptoms. For example, they might undergo testing for infection and even receive antibiotics even though no infection is found. Because people still have symptoms after treatment, doctors often take a sample of tissue for examination (biopsy), which will show eosinophils within the organ that is affected.
Treatment of these conditions frequently includes oral corticosteroids.
Hypereosinophilic syndrome is an uncommon disorder in which the number of eosinophils increases to more than 1,500 cells per microliter of blood (more than 1.5 × 109 per liter) for more than 6 months without an obvious cause. Some people have a rare chromosome disorder.
People of any age can develop hypereosinophilic syndrome, but it is more common in men older than 50. The increased number of eosinophils can damage the heart, lungs, liver, skin, and nervous system. For example, the heart can become inflamed in a condition called Löffler endocarditis, leading to formation of blood clots, heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , heart attacks Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount... read more , or malfunctioning heart valves Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more .
Symptoms may include weight loss, fevers, night sweats, fatigue, cough, chest pain, swelling, stomachache, rash, pain, weakness, confusion, and coma. Additional symptoms of this syndrome depend on which organs are damaged.
The syndrome is suspected when repeated blood tests reveal that the number of eosinophils is persistently increased in people who have these symptoms. The diagnosis is confirmed when doctors determine that the eosinophilia is not caused by a parasitic infection, an allergic reaction, or another diagnosable disorder and when biopsies show eosinophils within organs.
Without treatment, generally more than 80% of the people who have this syndrome die within 2 years, but with treatment, more than 80% survive. Heart damage is the principal cause of death. Some people need no treatment other than close observation for 3 to 6 months, but most need drug treatment with prednisone, hydroxyurea, or chemotherapy drugs.
Some people with hypereosinophilic syndrome have an acquired abnormality of a gene that regulates cell growth. This type of hypereosinophilia can respond to treatment with imatinib, a drug used to treat cancer. If treatment with these drugs is not successful, various other drugs may be used, and they can be combined with a procedure to remove eosinophils from the blood (leukapheresis Cytapheresis In apheresis, blood is removed from a person and then returned after substances are removed from it. Apheresis can be used to Obtain healthy blood components from a donor to transfuse to a person... read more ).