One of the major functions of erythrocytes is to carry oxygen to all parts of the body. In order to do this efficiently, there must be an adequate number of red blood cells and the red blood cells must contain an adequate supply of functioning hemoglobin. Erythrocyte tests include the red blood cell count, hematocrit, and hemoglobin. These tests are closely related and provide different ways to measure the adequacy of red blood cell production and function. Other common red blood cell tests include red blood cell indices
and the erythrocyte sedimentation rate.
and the erythrocyte sedimentation rate.
Red Blood Cell Count; Erythrocyte Count (RBC)
The red blood cell count identifies the number of red blood cells found in a cubic millimeter of blood (mm3) . The count is usually accomplished by an electronic or automated counting device.
Normal Range
Men
4.7-6.1 million/mm3
Women
4.2-5.4 million/mm3
Infants and Children
3 .8-5.5 million/mm.3
Newborns
4.8-7.1 million/mm3
Men
4.7-6.1 million/mm3
Women
4.2-5.4 million/mm3
Infants and Children
3 .8-5.5 million/mm.3
Newborns
4.8-7.1 million/mm3
Variations from Normal. A decrease in the number or function of red blood cells is called anemia. Factors that can cause anemia are decreased red blood cell production, increased red blood cell destruction, and blood loss.
Certain diseases can also cause a decrease in red blood cells. Some of these diseases include Hodgkin's disease, leukemia, rheumatic fever, and diseases that affect the bone marrow where red blood cells are produced.
An increase in the number of red blood cells is called erythrocytosis, a slight increase, or erythremia, an excessive increase. Many factors can contribute to this increase, such as an overproduction of red blood cells or a decrease in the amount of blood plasma. Conditions such as dehydration,
severe diarrhea, acute poisoning, and chronic lung disease can also cause an increase in the red blood cell count.
Certain diseases can also cause a decrease in red blood cells. Some of these diseases include Hodgkin's disease, leukemia, rheumatic fever, and diseases that affect the bone marrow where red blood cells are produced.
An increase in the number of red blood cells is called erythrocytosis, a slight increase, or erythremia, an excessive increase. Many factors can contribute to this increase, such as an overproduction of red blood cells or a decrease in the amount of blood plasma. Conditions such as dehydration,
severe diarrhea, acute poisoning, and chronic lung disease can also cause an increase in the red blood cell count.
Variations from Normal. A decrease in the number or function of red blood cells is called anemia. Factors that can cause anemia are decreased red blood cell production, increased red blood cell destruction, and blood loss.
Certain diseases can also cause a decrease in red blood cells. Some of these diseases include Hodgkin's disease, leukemia, rheumatic fever, and diseases that affect the bone marrow where red blood cells are produced.
An increase in the number of red blood cells is called erythrocytosis, a slight increase, or erythremia, an excessive increase. Many factors can contribute to this increase, such as an overproduction of red blood cells or a de crease in the amount of blood plasma. Conditions such as dehydration,
severe diarrhea, acute poisoning, and chronic lung disease can also cause an increase in the red blood cell count.
Certain diseases can also cause a decrease in red blood cells. Some of these diseases include Hodgkin's disease, leukemia, rheumatic fever, and diseases that affect the bone marrow where red blood cells are produced.
An increase in the number of red blood cells is called erythrocytosis, a slight increase, or erythremia, an excessive increase. Many factors can contribute to this increase, such as an overproduction of red blood cells or a de crease in the amount of blood plasma. Conditions such as dehydration,
severe diarrhea, acute poisoning, and chronic lung disease can also cause an increase in the red blood cell count.
Interfering Circumstances. The results of the red blood cell count can be altered by several nondisease situations. These would include the posture or position of the patient when the blood was drawn, exercise, age, altitude, pregnancy, and various legal and illegal drugs.
Hematocrit (Hct); Packed Cell Volume (PCV)
The purpose of the hematocrit or packed cell volume (PCV) test is to determine the percentage of red blood cells in whole blood. The hematocrit is reported as a percentage because it is the proportion of red blood cells compared
to the amount of plasma in whole blood.
The term "hematocrit" literally means to separate blood. A sample of blood is placed in a tube that contains an anticoagulant, which prevents clotting. The sample is mixed, and three distinct layers will separate out.
Figure 1-3 shows these three layers.
The bottom layer represents the hematocrit value and is composed of red blood cells, approximately 45% of the total blood volume, with variations allowed for men and women. The middle layer is a thin, whitish layer called the buffy coat, approximately 1% of the blood volume, which is made up of white blood cells and platelets . The upper layer is the liquid plasma, which comprises the remainder of the total blood volume.
Variations from Normal. Since the hematocrit is the percentage of red blood cells in whole blood, a decrease in hematocrit values is an indication of some type of anemia. Therefore, anything that causes a decrease in the number of red blood cells will result in a decrease in the hematocrit. Blood loss, conditions where there is increased destruction of red blood cells, leukemia, and diseases that interfere with red blood cell production will exhibit a low hematocrit. It must also be noted that overhydration, or an increase in plasma volume for any reason, can result in a relative decreased
hematocrit value.
An apparent increase in the hematocrit must be closely analyzed . Since the hematocrit is reported as a percentage of red blood cells to blood volume, any decrease in the volume of plasma would result in a mathematical increase in the hematocrit. Therefore, if the patient has lost blood plasma, the blood will be very concentrated and the hematocrit will be increased.
When an increase in hematocrit is related to the increase in the actual number of red blood cells, erythrocytosis or polycythemia is the result.
Interfering Circumstances. Factors that can influence hematocrit results include age, pregnancy, gender, and living in high altitudes.
Hemoglobin (Hgb) Hemoglobin is a protein-iron complex that is the main constituent of red blood cells. In fact, red blood cells contain approximately 90% hemoglobin.
The primary functions of hemoglobin are to transport oxygen from the lungs to the cells and to carry carbon dioxide from the cells to the lungs to be expelled. The hemoglobin test is used to indirectly evaluate the oxygen carrying capacity of the red blood cells. The hemoglobin count is also used
to diagnose, evaluate, or assess the treatment of various types of anemia.
Normal Range
Men 42-52%
Women 37-47% (in pregnancy: >33%)
Children 30-42%
Newborns 44-64%
to the amount of plasma in whole blood.
The term "hematocrit" literally means to separate blood. A sample of blood is placed in a tube that contains an anticoagulant, which prevents clotting. The sample is mixed, and three distinct layers will separate out.
Figure 1-3 shows these three layers.
The bottom layer represents the hematocrit value and is composed of red blood cells, approximately 45% of the total blood volume, with variations allowed for men and women. The middle layer is a thin, whitish layer called the buffy coat, approximately 1% of the blood volume, which is made up of white blood cells and platelets . The upper layer is the liquid plasma, which comprises the remainder of the total blood volume.
Variations from Normal. Since the hematocrit is the percentage of red blood cells in whole blood, a decrease in hematocrit values is an indication of some type of anemia. Therefore, anything that causes a decrease in the number of red blood cells will result in a decrease in the hematocrit. Blood loss, conditions where there is increased destruction of red blood cells, leukemia, and diseases that interfere with red blood cell production will exhibit a low hematocrit. It must also be noted that overhydration, or an increase in plasma volume for any reason, can result in a relative decreased
hematocrit value.
An apparent increase in the hematocrit must be closely analyzed . Since the hematocrit is reported as a percentage of red blood cells to blood volume, any decrease in the volume of plasma would result in a mathematical increase in the hematocrit. Therefore, if the patient has lost blood plasma, the blood will be very concentrated and the hematocrit will be increased.
When an increase in hematocrit is related to the increase in the actual number of red blood cells, erythrocytosis or polycythemia is the result.
Interfering Circumstances. Factors that can influence hematocrit results include age, pregnancy, gender, and living in high altitudes.
Hemoglobin (Hgb) Hemoglobin is a protein-iron complex that is the main constituent of red blood cells. In fact, red blood cells contain approximately 90% hemoglobin.
The primary functions of hemoglobin are to transport oxygen from the lungs to the cells and to carry carbon dioxide from the cells to the lungs to be expelled. The hemoglobin test is used to indirectly evaluate the oxygen carrying capacity of the red blood cells. The hemoglobin count is also used
to diagnose, evaluate, or assess the treatment of various types of anemia.
Normal Range
Men 42-52%
Women 37-47% (in pregnancy: >33%)
Children 30-42%
Newborns 44-64%
A normal red blood cell count does not automatically translate into a normal hemoglobin value. Abnormal production of any portion of hemoglobin could result in decreased levels of hemoglobin per red blood cells.
Once a sample of blood is taken, the hemoglobin level is determined by automated electronic equipment. Generally, the hemoglobin value is approximately one-third of the hematocrit value. Therefore, a person with a 45% hematocrit would be expected to have approximately 15 grams of hemoglobin per deciliter of blood (15 g/dl).
Once a sample of blood is taken, the hemoglobin level is determined by automated electronic equipment. Generally, the hemoglobin value is approximately one-third of the hematocrit value. Therefore, a person with a 45% hematocrit would be expected to have approximately 15 grams of hemoglobin per deciliter of blood (15 g/dl).
Normal Range
Men
14-18 g/dl
Women
12-16 g/dl (in pregnancy: >11 g/dl)
Children
11-16 g/dl
Newborns
14-24 g/dl
Men
14-18 g/dl
Women
12-16 g/dl (in pregnancy: >11 g/dl)
Children
11-16 g/dl
Newborns
14-24 g/dl
Variations from Normal. Hemoglobin levels can exhibit temporary variations immediately after blood transfusions, hemorrhages, and burns. A decrease in the hemoglobin level can be found in various anemias. Other diseases and factors that result in a hemoglobin decrease include hyperthyroidism, cirrhosis of the liver, transfusions of incompatible blood, Hodgkin's disease, lymphoma, and reactions to various chemicals and drugs. Since iron
is necessary for the production of hemoglobin, a decreased hemoglobin level may signal the need for blood iron tests. Blood Chemistry Tests.
An increase in hemoglobin levels is found in any situation that results in an increased number of healthy red blood cells. Diseases associated with increased hemoglobin values are chronic obstructive pulmonary disease
and congestive heart failure .
Interfering Circumstances. Factors that can affect hemoglobin results include pregnancy, altitude, age, gender, and excessive fluid intake. Various medications may cause an increase or decrease in hemoglobin levels.
is necessary for the production of hemoglobin, a decreased hemoglobin level may signal the need for blood iron tests. Blood Chemistry Tests.
An increase in hemoglobin levels is found in any situation that results in an increased number of healthy red blood cells. Diseases associated with increased hemoglobin values are chronic obstructive pulmonary disease
and congestive heart failure .
Interfering Circumstances. Factors that can affect hemoglobin results include pregnancy, altitude, age, gender, and excessive fluid intake. Various medications may cause an increase or decrease in hemoglobin levels.
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