Blood transfusion is the taking of blood or blood-based products from
one individual and inserting them into the circulatory system of
another. It can be considered a form of organ transplant. It is
performed as a treatment for various medical conditions, such as
massive blood loss due to trauma, surgery, shock and other conditions
in which tissues of the body are not adequately oxygenated, where
carbon dioxide or other toxic materials are not being effectively
removed, and where the red cell producing mechanism (or some other
normal and essential component) fails.
Great care is taken to ensure that the recipient's immune system is
compatible with the foreign blood, and also that the foreign blood is
compatible with the donor's immune system. In addition to the
familliar human blood type (A, B, AB and O) classifications and the
Rhesus factor classification (positive or negative), today a number of
other tissue type factors are also known to determine
histocompatibility, to one degree or other. These tissue type factors
become increasingly important in people who receive many blood
transfusions as their bodies develop increasing resistance to blood
from other people.
There is increased awareness that a number of diseases (such as AIDS,
human T-Cell lymphotropic virus which causes a form of leukemia,
syphilis, hepatitis B and hepatitis C) can be passed from the blood
donor to the transfusion recipient, and tight human blood transfusion
standards are the rule in all developed countries. Standards include
screening for potential risk factors and health problems through such
steps as the taking of blood pressure, determining if the donor has
enough hemoglobin (the iron-containing protein in blood cells which
enables efficient transport of oxygen), and answering a set of
standard oral and written questions, as well as testing donated units
for these infections. The lack of such standards in places like rural
China, where desperate villagers donated plasma for money and had
others' red blood cells reinjected, has produced entire villages
infected with the AIDS virus.
Blood substitutes that will avoid this risk, address the chronic blood
donor shortage and address some religious objections of groups such as
the Jehovah's Witnesses, are currently in the clinical evaluation
stage. Most attempts to find a suitable alternative to blood have so
far concentrated on cell-free haemoglobin solutions.
The entire process of donating blood takes about 45 minutes. About 450
ml (? pint) is taken. Afterwards, the consumption of moderate amounts
of non-alcoholic liquid refreshments is encouraged, as this assists
with fluid replacement which occurs within a few hours. Other
components are replaced by the donor's own body within a few days or
Depending on the needs of the community at any one time sometimes only
parts of the blood are taken as a donation. Blood is made up mostly of
red blood cells, platelets - essential in the normal clotting
mechanism, and plasma. The latter two can be donated separately in a
process called ~apherisis. Blood is often separated into components
after being donated. These components also include albumin protein
used to treat burns, clotting factor concentrates used to treat
hemophilia, cryoprecipitate, and immunoglobulin antibodies for
In cases where whole blood is donated, there is no transfusion-related
risk of illness for the blood donor, aside from the minuscule chance
of infection or perhaps of localized injury to the donor site. There
is some risk to the donor in cases where the donor donates plasma and
has red blood cells reinfused. This risk is nonexistent in cases where
proper sterilization procedures are followed, but has caused public
health disasters in China where they were often unregulated. The
best-known examples of safe apheresis donation are the United States'
blood plasma collection centers, maintained by pharmaceutical
companies, using paid donors up to twice-weekly.
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Donations are usually anonymous to the recipient, but products in a
blood bank are always individually traceable through the whole cycle
of donation, testing, separation into components, storage,
administration to the recipient, and any resultant disease.
It is interesting to note that veterinarians occasionally administer
transfusions to animals in need of this treatment. Various species
require different levels of testing to ensure a compatible match. Cats
have 3 blood types, cattle have 11, dogs have a dozen, pigs 16 and
horses have 34.
The rare and experimental practice of inter-species blood transfusions
is a form of xenograft.
Research into blood substitutes which could make blood transfusions
more readily available in emergency medicine and even in pre-hospital
EMS care continues. If successful such a blood substitute could save
many lives, particularly in traumas where massive blood loss results.
While it is not strictly a type blood transfusion, the formal practice
of sealing a long term relationship through the co-mingling of blood
to become blood brothers should be mentioned. This is a social ritual
or custom, with no medical justification or indication. The practice
carries with it a slight risk of blood born illness, infection or
Research into blood transfusion began in the 7th century with
successful experiments of transfusions between animals, but successive
attempts on humans usually brought death.
Only in the first decade of the 1900s was the reason for such death
found in the existence of blood types, and the practice of mixing some
blood from the donor and the receiver before the transfusion allowed a
greater number of successes.
While the first transfusions had to be made directly from donor to
receiver before coagulation, in the 1910s it was discovered that by
adding anticoagulants and refrigerating the blood it was possible to
store it for some days, thus opening the way for blood banks.