EP test


erythrocyte

 [ĕ-rith´ro-sīt] one of the formed elements in the blood" >peripheral blood, constituting the great majority of the cells in the blood. (For immature forms see series" >erythrocytic series.) In humans the normal mature erythrocyte is a biconcave disk without a nucleus, about 7.7 micrometers in diameter, consisting mainly of hemoglobin and a supporting framework called the stroma. Erythrocyte formation (erythropoiesis) takes place in the red bone marrow in the adult, and in the liver, spleen, and bone marrow of the fetus. It requires an ample supply of dietary elements such as iron, cobalt, copper, amino acids, and certain vitamins. Called also red cell or corpuscle and red blood cell or corpuscle.ƒ
The functions of erythrocytes include transportation of oxygen and carbon dioxide. They owe their oxygen-carrying ability to hemoglobin, a combination of an iron-containing prosthetic group (heme) with a protein (globin). Hemoglobin attracts and forms a loose connection with free oxygen, and its presence enables blood to absorb some 60 times the amount of oxygen that the plasma by itself absorbs. Oxyhemoglobin is red, which gives oxygenated blood its red color. Erythrocytes are stored in the spleen, which acts as a reservoir for the blood system and discharges the cells into the blood as required. The spleen may discharge extra erythrocytes into the blood during emergencies such as hemorrhage or shock.
Erythrocytes also are important in the maintenance of a normal acid-base balance, and, since they help determine the viscosity of the blood, they also influence its specific gravity. Their average life span is 120 days. They are subjected to much wear and tear in circulation and eventually are removed by cells of the reticuloendothelial system, particularly in the liver, bone marrow, and spleen. In spite of this constant destruction and production of erythrocytes, the body maintains a fairly constant number, between 4 and 5 million per mm3 of blood in women and 5 to 6 million per mm3 in men. A decreased number constitutes one form of anemia.
Erythrocytes are destroyed whenever they are exposed to solutions that are not isotonic to blood plasma. If they are placed in a solution that is more dilute than plasma (distilled water for example) the cells will swell until osmotic pressure bursts the cell membrane. If they are placed in a solution more concentrated than plasma, the cells will lose water and shrivel or crenate. It is for this reason that solutions to be given intravenously must be isotonic to plasma.
Aged red cells are ingested by macrophages in the spleen and liver. The iron is transported by the plasma protein transferrin to the bone marrow, where it is incorporated into new red cells. The heme group is converted to bilirubin, a bile pigment secreted by the liver. About 180 million red blood cells are destroyed every minute. Since the number of cells in the blood remains more or less constant, this means that about 180 million red blood cells are manufactured every minute.
Determination of the red blood cell volume is usually done as a preliminary step in determination of the total blood volume. A radioactive substance, usually chromium, is used to “tag” cells of a sample of blood drawn from the patient. The sample is then reintroduced into the circulating blood and subsequent samples are taken to be evaluated for degree of radioactivity. The degree of dilution is used to calculate total blood volume.The events in the life of erythrocytes. Nucleated red blood cell (RBC) precursors stimulated by erythropoietin form erythrocytes in the bone marrow. Normal synthesis of hemoglobin occurs only in the presence of nutrients, iron, vitamin B12, and folic acid. Mature RBCs are released into circulation. The old or defective RBCs are degraded in the spleen. Iron and globin are reutilized immediately. Bilirubin is released in bile into the intestine. From Damjanov, 1996.erythrocyte protoporphyrin test EP test; a screening test for lead toxicity; erythrocyte protoporphyrin levels are determined by direct fluorometry of whole blood or fluorescence analysis of whole blood extracts. Levels will be increased in either lead poisoning or iron deficiency.erythrocyte sedimentation rate the rate at which erythrocytes settle out of unclotted blood in one hour. The test is based on the fact that inflammatory processes cause an alteration in blood proteins, resulting in aggregation of the red cells, which makes them heavier and more likely to fall rapidly when placed in a special vertical test tube. Normal ranges vary according to the type of tube used, each type being of a different size. The most common methods and the normal range for each are: Wintrobe method, 0 to 6.5 mm per hour for men, 0 to 15 mm per hour for women; and Westergren method, 0 to 15 mm per hour for men, 0 to 20 mm per hour for women.ƒ
The erythrocyte sedimentation rate is often inconclusive and is not considered specific for any particular disorder. It is most often used as a gauge for determining the progress of an inflammatory disease such as rheumatic fever, rheumatoid arthritis, or a respiratory infection. The information provided by this test must be used in conjunction with results from other tests and clinical evaluations.