APPENDIX 5 |
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BLOOD COUNTA blood count is a laboratory test that measures the number and characteristics of the red and white blood cells and the platelets in a drop of blood.
Red blood cells carry oxygen from inhaled air in the lungs to all parts of the body and return carbon dioxide to the child's lungs for elimination through the exhaled air.
White blood cells fight infection and perform many other functions. The white blood cell count may help to determine if a child's infection is viral or bacterial by the total number of cells. A high white blood cell count suggests a bacterial infection that may be helped by antibiotics. A low white blood cell count may indicate a virus disease, which usually does not respond to antibiotics.
Platelets are small white blood cells that play an important role in blood clotting.
The blood count is done in several parts, including the hematocrit, the hemoglobin, and the blood smear.
The hematocrit measures the proportion of red cells in a unit of blood. This test is done with blood in a centrifuge (a machine that spins its contents at a very rapid speed for the purpose of separating substances of differing densities). When the tube is spun, the blood is separated into the cells and the plasma. The proportion of the centrifuged column of blood occupied by the red blood cells is known as the hematocrit.
The hemoglobin test measures the quantity of hemoglobin (the red chemical contained in the red blood cells that binds oxygen and carbon dioxide) in a unit volume of blood.
The blood smear measures a number of components, including the number of white cells per cubic centimeter of blood and the differential white count (the proportion of the various kinds of white cells present). A drop of blood is placed on a glass slide and spread thin. The smear is stained with a special dye that colors the red blood cells, the white blood cells, and the platelets, making them more visible. One hundred white blood cells are counted and classified according to cell type. The shape, size, and intensity of coloration of the red blood cells and the number of platelets can also be determined.
Blood counts frequently help establish a precise diagnosis. However, the history of the illness and the physical examination are equally important.
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