Variations in the structure and function of blood cells may not only cause
disease, but may also occur as a result of a disease process . In health, mature,
functioning blood cells enter the bloodstream and are able to carry out
the work of the blood. In disease, immature, poorly formed cells may be
found in the blood and are often unable to carry out the work of the blood.
Blood Cell Tests
The blood cell tests presented in this chapter focus on cell number, size, or
structure . Tests are presented by individual cell type and include diagnoses
related to variations from normal.
Normal ranges of blood cell tests depend on a variety of factors including
the age of the individual being tested and the individual laboratory standards
where the tests are run. There are a variety of factors that may cause an
abnormal test result. These factors are listed with the description of each test.
Dec 1, 2010
Variations in the Number ofBlood Cells
The blood cell tests deal primarily with variations in the
number of each type of blood cell. The results of these tests may not identify
a specific disease, but they do provide valuable information about the patient's
condition.
There are several general terms associated with the increase or decrease
in the number of each type of blood cell. An overview of these terms is presented
here. The diagnostic significance of this information is detailed in
the discussion of each individual blood cell test.
number of each type of blood cell. The results of these tests may not identify
a specific disease, but they do provide valuable information about the patient's
condition.
There are several general terms associated with the increase or decrease
in the number of each type of blood cell. An overview of these terms is presented
here. The diagnostic significance of this information is detailed in
the discussion of each individual blood cell test.
Variations in the Number of Erythrocytes
Red blood cell disorders are classified as anemia, erythrocytosis, and erythremia.
Anemia is defined as a reduction in the number of circulating red
blood cells due to blood loss; a decreased production of red cells; an increased
destruction of red blood cells; or a deficiency of hemoglobin. Erythrocytosis
is defined as a slight increase in circulating red blood cells,
while erythremia is an excessive increase in circulating red blood cells.
Variations in the number of circulating red blood cells can be caused by
a variety of conditions. However, if the clinician suspects that there is a
problem with the production of red blood cells, a bone marrow aspiration
may be ordered. Bone marrow can be withdrawn from the posterior iliac
crest, anterior iliac crest, and the sternum. Bone marrow aspiration is performed
by a physician and requires written consent from the patient or the
patient's legal representative.
Anemia is defined as a reduction in the number of circulating red
blood cells due to blood loss; a decreased production of red cells; an increased
destruction of red blood cells; or a deficiency of hemoglobin. Erythrocytosis
is defined as a slight increase in circulating red blood cells,
while erythremia is an excessive increase in circulating red blood cells.
Variations in the number of circulating red blood cells can be caused by
a variety of conditions. However, if the clinician suspects that there is a
problem with the production of red blood cells, a bone marrow aspiration
may be ordered. Bone marrow can be withdrawn from the posterior iliac
crest, anterior iliac crest, and the sternum. Bone marrow aspiration is performed
by a physician and requires written consent from the patient or the
patient's legal representative.
Variations in the Number of Leukocytes
White blood cell disorders fall into one of two categories: leukocytosis, a
slight increase in the number of white cells, or leukopenia (leukocytopenia),
a decrease in the number of white cells. Since there are many types of
white blood cells, the cell count of each specific type can indicate a variety
of problems or diagnoses . Specific cell counts and their diagnostic significance
are presented with each blood cell test.
White blood cell disorders fall into one of two categories: leukocytosis, a
slight increase in the number of white cells, or leukopenia (leukocytopenia),
a decrease in the number of white cells. Since there are many types of
white blood cells, the cell count of each specific type can indicate a variety
of problems or diagnoses . Specific cell counts and their diagnostic significance
are presented with each blood cell test.
Variations in the Number of Thrombocytes
Thrombocyte or platelet disorders are classified as thrombocytopenia, a decrease
in the number of platelets, or thrombocytosis, a slight increase in the
number of platelets . An excessive increase in the number of platelets is often
referred to as thrombocythemia. Variations in the number of thrombocytes
can be the result of bone marrow disorders. Thrombocytopenia is the most
common cause of bleeding disorders. Thrombocytosis can be the result of a
variety of conditions such as acute blood loss, following splenectomy, some
anemias, and chronic diseases. Other causes of thrombocytosis are related to
specific hematological disorders, such as autoimmune hemolytic anemia.
in the number of platelets, or thrombocytosis, a slight increase in the
number of platelets . An excessive increase in the number of platelets is often
referred to as thrombocythemia. Variations in the number of thrombocytes
can be the result of bone marrow disorders. Thrombocytopenia is the most
common cause of bleeding disorders. Thrombocytosis can be the result of a
variety of conditions such as acute blood loss, following splenectomy, some
anemias, and chronic diseases. Other causes of thrombocytosis are related to
specific hematological disorders, such as autoimmune hemolytic anemia.
Blood Collection Procedures
There are two basic types of blood collection procedures: skin (dermal)
puncture and venipuncture. Skin puncture is used to collect capillary blood.
The puncture site for adults and children is usually the fingertip, and for infants
the sites are the heel or the great toe. Venipuncture is necessary for
most diagnostic tests. As the name implies, blood is withdrawn from a vein
through the use of a needle and special collection tube or syringe.
puncture and venipuncture. Skin puncture is used to collect capillary blood.
The puncture site for adults and children is usually the fingertip, and for infants
the sites are the heel or the great toe. Venipuncture is necessary for
most diagnostic tests. As the name implies, blood is withdrawn from a vein
through the use of a needle and special collection tube or syringe.
Composition of Blood
The average adult has about 5 liters (5-6 quarts) of blood, which is divided
into plasma and cells. Plasma, which accounts for about 3 liters, is the liquid
portion of blood. The cells, which account for about 2 liters, are referred
to as the formed elements or cellular component of blood.
Blood Cells
into plasma and cells. Plasma, which accounts for about 3 liters, is the liquid
portion of blood. The cells, which account for about 2 liters, are referred
to as the formed elements or cellular component of blood.
Blood Cells
Blood cells are classified as erythrocytes (red blood cells), leukocytes (white
blood cells), and thrombocytes, also called platelets. Each type of blood cell
has specific functions. A brief description of the cell, its functions, and
unique characteristics follows.
blood cells), and thrombocytes, also called platelets. Each type of blood cell
has specific functions. A brief description of the cell, its functions, and
unique characteristics follows.
Erythrocytes:
Erythrocytes are the most numerous cells, second in size, and
easily identified by their unique biconcave disk shape. Red blood cells are
formed in the red bone marrow, live about 120 days, and are removed from
the blood stream by phagocytes, cells that are able to engulf and digest cellular
debris. The spleen is the primary site of phagocytosis of aged red
blood cells. The liver and bone marrow also play a role in removing or recycling
red blood cells.
The main functions of erythrocytes are to carry oxygen to all parts of
the body and to bring carbon dioxide to the lungs. The hemoglobin in the
red blood cell is the carrier for oxygen and carbon dioxide . Therefore, in
order for oxygen and carbon dioxide to move throughout the body, an adequate
number of mature, functioning red blood cells must be available .
The red blood cells must also contain the appropriate amount of hemoglobin.
easily identified by their unique biconcave disk shape. Red blood cells are
formed in the red bone marrow, live about 120 days, and are removed from
the blood stream by phagocytes, cells that are able to engulf and digest cellular
debris. The spleen is the primary site of phagocytosis of aged red
blood cells. The liver and bone marrow also play a role in removing or recycling
red blood cells.
The main functions of erythrocytes are to carry oxygen to all parts of
the body and to bring carbon dioxide to the lungs. The hemoglobin in the
red blood cell is the carrier for oxygen and carbon dioxide . Therefore, in
order for oxygen and carbon dioxide to move throughout the body, an adequate
number of mature, functioning red blood cells must be available .
The red blood cells must also contain the appropriate amount of hemoglobin.
Leukocytes:
Leukocytes are the largest in size and represent the fewest number
of blood cells. There are two major types of leukocytes: granulocytes and
agranulocytes. Granulocytes, also called polymorphonuclear leukocytes
(PMNs), are the most numerous and have dark-staining granules in the cytoplasm.
These cells are further classified as neutrophils, eosinophils, and basophils.
Agranulocytes, also called mononuclear leukocytes, do not have
dark-staining granules in the cytoplasm. Agranulocytes are further classified
as lymphocytes or monocytes.
Leukocytes are chiefly responsible for fighting infection by identifying,
engulfing, and destroying foreign organisms . They are active in the immune
response by producing antibodies to foreign organisms. Additional infor
mation about the function of each type of leukocyte is discussed with the
blood cell tests related to the specific type of leukocyte.
of blood cells. There are two major types of leukocytes: granulocytes and
agranulocytes. Granulocytes, also called polymorphonuclear leukocytes
(PMNs), are the most numerous and have dark-staining granules in the cytoplasm.
These cells are further classified as neutrophils, eosinophils, and basophils.
Agranulocytes, also called mononuclear leukocytes, do not have
dark-staining granules in the cytoplasm. Agranulocytes are further classified
as lymphocytes or monocytes.
Leukocytes are chiefly responsible for fighting infection by identifying,
engulfing, and destroying foreign organisms . They are active in the immune
response by producing antibodies to foreign organisms. Additional infor
mation about the function of each type of leukocyte is discussed with the
blood cell tests related to the specific type of leukocyte.
Thrombocytes:
Thrombocytes, also called platelets, are essential for coagulation.
Without an adequate number of functioning platelets, an individual
would bleed to death.
Without an adequate number of functioning platelets, an individual
would bleed to death.
Plasma
Plasma, the fluid or liquid component of blood, is about 90% water. The
remaining constituents of plasma include a variety of substances either
dissolved or suspended in this watery medium: proteins; minerals such
as calcium, potassium, and sodium; glucose; lipids; cholesterol; and
waste products. Other components include antibodies, enzymes, and hormones.
The primary functions of plasma are to transport nutrients and other
necessary chemicals to all body cells and to bring waste products to the
body systems and organs that serve as waste disposal centers.
remaining constituents of plasma include a variety of substances either
dissolved or suspended in this watery medium: proteins; minerals such
as calcium, potassium, and sodium; glucose; lipids; cholesterol; and
waste products. Other components include antibodies, enzymes, and hormones.
The primary functions of plasma are to transport nutrients and other
necessary chemicals to all body cells and to bring waste products to the
body systems and organs that serve as waste disposal centers.
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