WHOLE
BLOOD AND BLOOD COMPONENTS
Background
Blood may be transfused as whole blood or as one of its components. Because patients
seldom require all of the components of whole blood, it makes sense to transfuse only that
portion needed by the patient for a specific condition or disease. This treatment,
referred to as “blood component therapy,” allows several patients to benefit
from one unit of donated whole blood. Blood components include red blood cells, plasma,
platelets and cryoprecipitated antihemophilic factor (AHF). Up to four components may be
derived from one unit of blood. Improvements in cell preservative solutions over the last
15 years have increased the shelf-life of red blood cells from 21 to 42 days.
Whole blood
is a living tissue that circulates through the heart, arteries, veins and capillaries
carrying nourishment, electrolytes, hormones, vitamins, antibodies, heat and oxygen to the
body's tissues. Whole blood contains red blood cells, white blood cells and platelets
suspended in a proteinaceous fluid called plasma.
If blood is treated to prevent clotting and permitted to stand in a container, the red
blood cells, weighing the most, will settle to the bottom; the plasma will stay on top;
and the white blood cells and platelets will remain suspended between the plasma and the
red blood cells. A centrifuge may be used to hasten this separation process. The
platelet-rich plasma is then removed and placed into a sterile bag, and it can be used to
prepare platelets and cryoprecipitated AHF. To make platelets, the platelet-rich plasma is
centrifuged, causing the platelets to settle at the bottom of the bag. Plasma and
platelets are then separated and made available for transfusion. The plasma may also be
pooled with plasma from other donors and further processed, or fractionated, to provide
purified plasma proteins such as albumin, immunoglobulin and clotting factors.
Red blood
cells are perhaps the most recognizable component of whole
blood. Red blood cells contain hemoglobin, a complex iron-containing protein that carries
oxygen throughout the body and gives blood its red color. The percentage of blood volume
composed of red blood cells is called the “hematocrit.” The average hematocrit
in an adult male is 47 percent. There are about one billion red blood cells in two to
three drops of blood, and, for every 600 red blood cells, there are about 40 platelets and
one white cell. Manufactured in the bone marrow, red blood cells are continuously being
produced and broken down. They live for approximately 120 days in the circulatory system
and are eventually removed by the spleen.
Red blood cells are prepared from whole blood by removing the plasma, or the liquid
portion of the blood, and can raise the patient's hematocrit and hemoglobin levels while
minimizing an increase in blood volume.
Patients who benefit most from transfusions of red blood cells include those with
chronic anemia resulting from kidney failure, malignancies, or gastrointestinal bleeding
and those with acute blood loss resulting from trauma. Since red blood cells have reduced
amounts of plasma, they are well-suited for treating anemia patients who would not
tolerate the increased volume provided by whole blood, such as patients with congestive
heart failure or those who are elderly or debilitated.
Red blood cells may be treated and frozen for extended storage (up to 10 years).
Plasma
is the liquid portion of the blood--a protein-salt solution in which
red and white blood cells and platelets are suspended. Plasma, which is 90 percent water,
constitutes 55 percent of blood volume. Plasma contains albumin (the chief protein
constituent), fibrinogen (responsible, in part, for the clotting of blood), and globulins
(including antibodies). Plasma serves a variety of functions, from maintaining a
satisfactory blood pressure and volume to supplying critical proteins for blood clotting
and immunity. It also serves as the medium of exchange for vital minerals such as sodium
and potassium, thus helping maintain a proper balance in the body, which is critical to
cell function. Plasma is obtained by separating the liquid portion of blood from the
cells.
Fresh frozen plasma is frozen within hours after donation to preserve clotting factors,
stored for one to seven years, and thawed before it is transfused. It is most often used
to treat certain bleeding disorders for which no factor-specific concentrate is available,
but it can also be used for plasma replacement via a process called plasma exchange.
Cryoprecipitated
AHF is the portion of plasma that is rich in certain clotting
factors, including Factor VIII, fibrinogen, von Willebrand factor and Factor XIII.
Cryoprecipitated AHF is removed from plasma by freezing and then slowly thawing the
plasma. It is used to prevent or control bleeding in individuals with hemophilia and von
Willebrand syndromes, which are the most common, inherited major coagulation
abnormalities. Its use in these conditions is reserved for when viral-inactivated
concentrates containing Factor VIII and von Willebrand factor are unavailable and plasma
derivatives must be used.
Platelets
(or thrombocytes) are very small cellular components of blood that help the clotting
process by sticking to the lining of blood vessels. Platelets are made in the bone marrow
and survive in the circulatory system for an average of 9-10 days before being removed
from the body by the spleen. The platelet is vital to life, because it helps prevent both
massive blood loss resulting from trauma and blood vessel leakage that would otherwise
occur in the course of normal, day-to-day activity. Units of platelets are prepared by
using a centrifuge to separate the platelet-rich plasma from the donated unit of whole
blood. The platelet-rich plasma is then centrifuged again to concentrate the platelets
further.
Platelets may also be obtained from a donor by a process known as apheresis, or
plateletpheresis. In this process, blood is drawn from the donor into an apheresis
instrument, which, using centrifugation, separates the blood into its components, retains
the platelets, and returns the remainder of the blood to the donor. The resulting
component contains about six times as many platelets as a unit of platelets obtained from
whole blood. Platelets are used to treat a condition called thrombocytopenia, in which
there is a shortage of platelets, and in patients with abnormal platelet function.
Platelets are stored at room temperature for up to five days.
White blood
cells are responsible for protecting the body from invasion
by foreign substances such as bacteria, fungi and viruses. One form of white blood cells,
called lymphocytes, aid in the immune defense. The majority of white blood cells
are produced in the bone marrow, where they outnumber red blood cells by two to one.
However, in the blood stream, there are about 600 red blood cells for every white blood
cell. There are several types of white blood cells. Granulocytes and macrophages protect
against infection by surrounding and destroying invading bacteria and viruses, and
lymphocytes aid in the immune defense.
Granulocytes are prepared by apheresis or by centrifugation of whole blood. They are
transfused within 24 hours after collection and are used for infections that are
unresponsive to antibiotic therapy. The effectiveness of white blood cell transfusion is
still being investigated.
Plasma
derivatives are concentrates of specific plasma proteins that
are prepared from pools (many units) of plasma. Plasma derivatives are obtained through a
process, known as fractionation, developed during World War II, and are heat-treated
and/or solvent detergent- treated to kill certain viruses, including those that cause AIDS
and hepatitis B and C. Plasma derivatives include:
- Factor VIII Concentrate
- Factor IX Concentrate
- Anti-Inhibitor Coagulation Complex (AICC)
- Albumin
- Immune Globulins, including Rh Immune
Globulin
- Anti-Thrombin III Concentrate
- Alpha 1-Proteinase Inhibitor Concentrate
