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HEMOGLOBIN DETERMINATION A routine test performed on practically every patient is the hemoglobin determination. Hemoglobin determination, or hemoglobinometry, is the measurement of the concentration of hemoglobin in the blood. Hemoglobin's main function in the body is to carry oxygen from the lungs to the tissues and to assist in transporting carbon dioxide from the tissues to the lungs. The formation of hemoglobin takes place in the developing red cells located in bone marrow. Hemoglobin values are affected by age, sex, pregnancy, disease, and altitude. During pregnancy, gains in body fluids cause the red cells to become less concentrated, causing the red cell count to fall. Since hemoglobin is contained in red cells, the hemoglobin concentration also falls. Disease may also affect the values of hemoglobin. For example, iron deficiency anemia may drop hemoglobin values from a normal value of 14 grams per 100 milliliters to 7 grams per 100 milliliters. Above-normal hemoglobin values may occur when dehydration develops. Changes in altitude affect the oxygen content of the air and, therefore, also affect hemoglobin values. At higher altitudes there is less oxygen in the air, resulting in an increase in red cell counts and hemoglobin values. At lower altitudes there is more oxygen, resulting in a decrease in red cell counts and hemoglobin values.
Figure 7-14.-Loading hemacytometer: A. Hemacytometer properly loaded; B. Hemacytometer improperly loaded.
Figure 7-15-Loaded hemacytometer placed inside petri dish. Figure 7-16.-Hemacytometer
counting chamber.
Methods for hemoglobin determination are many and varied. The most widely used automated method is the cyanmethemoglobin method. To perform this method, blood is mixed with Drabkin's solution, a solution that contains ferricyanide and cyanide. The ferricyanide oxidizes the iron in the hemoglobin, thereby changing hemoglobin to methemoglobin. Methemoglobin then unites with the cyanide to form cyanmethemoglobin. Cyanmethemoglobin produces a color which is measured in a colorimeter, spectrophotometer, or automated instrument. The color relates to the concentration of hemoglobin in the blood. Manual methods for determining blood hemoglobin include the Haden-Hausse and Sahli-Hellige methods. In both methods, blood is mixed with dilute hydrochloric acid. This process hemolyzes the red cells, disrupting the integrity of the red cells' membrane and causing the release of hemoglobin, which, in turn, is converted to a brownish-colored solution of acid hematin. The acid hematin solution is then compared with a color standard. |
 
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