The blood consists of different types of cells including red blood cells, white blood cells and platelets. White blood cells are part of the body’s immune system and serve to defend the body against microorganisms and other foreign substances. Five different types of white blood cells exist, one of which is the eosinophil. Healthy bodies contain a specified number of eosinophils. Abnormal numbers often indicate the presence of disease.
Cells consist of numerous structures, two of which are the nucleus and the cytoplasm. The nucleus stores the cell’s genetic information, and the cytoplasm is the substance outside the nucleus. A process called staining allows one to identify cell types and differentiate cellular structures when the stained specimen is viewed using a microscope. The cytoplasm of eosinophils contains course granules that appear reddish-orange when stained with the dye eosin. Rather than being spherical, the nucleus of the eosinophil typically consists of two lobes.
Function of Eosinophils
Eosinophils play a specific role within the immune system. They are particularly efficient at destroying foreign substances that may present within the body as a result of parasitic infections. Eosinophils also serve to encourage inflammation. Inflammation is not necessarily a bad thing. It is the body’s way of naturally isolating and controlling a disease site. Unfortunately, inflammation can also cause damage to the tissues of the body. Consequently, in addition to examining blood, physicians often stain and examine inflamed tissue for the presence of eosinophils as a means of determining the cause of inflammation.
Measuring Eosinophil Number
A complete blood count, or CBC, is a blood test that determines the number of various cells in the blood, including eosinophils. Values obtained can be either relative or absolute. A relative count is the number of eosinophils present for every 100 white blood cells counted and is expressed as a percentage. Absolute eosinophil levels are determined by multiplying the relative value by the total white cell count. According to David Zwick, M.D., of the Children’s Mercy Hospitals and Clinics, relying on percentages rather than absolute values can result in misinterpretation of abnormalities. Consequently, many laboratories report both relative and absolute values.
Normal Eosinophil Levels
According to the Merck Manual, a value of 1 to 4 percent eosinophils is considered a normal relative range and 50 to 400 eosinophils per cubic millimeter of blood represents a normal absolute range. In her book entitled, “Blood Cells: A Practical Guide,” Barbara J. Bain, professor of diagnostic haemotology at Imperial College in London, states that normal absolute eosinophil values are the same for men and women, as well as individuals of different ethnic groups. Absolute eosinophil counts are higher in newborns than adults. A slow decline in absolute eosinophil levels is seen in the elderly.
Abnormal Eosinophil Levels
Eosinophelia is the term used to describe abnormally high absolute eosinophil levels. Intestinal parasitic infections, such as those caused by roundworms or tapeworms, certain types of leukemia, autoimmune conditions, such as lupus, allergies, and asthma are conditions associated with high absolute eosinophil levels. According to the National Institutes of Health, medications such as amphetamines, laxatives containing psyllium, certain antibiotics, interferon, and tranquilizers can cause eosinophelia. They also claim that lower than normal absolute eosinophil levels may result from alcohol intoxication and the presence of too much cortisol (a hormone produced by the adrenal glands) in the body.