When
blood is given to a person
intravenously.
The majority of blood
transfusions are called
allogenic transufions, meaning the blood has come from someone other than the
patient.
A transfusion where the patient recieves blood they have given ahead of time is called an
autologous transfusion.
Who needs a blood transufion:
Those who have lost a significant amout of blood in an accident or during a surgery.
Those who are on chemotherapy, since their bone marrow may not be capable of making new blood cells.
Those with anemia, who's blood does not have enough hemoglobin.
Risks of recieving a transfusion:
Getting AIDS or HIV.
Getting Hepatitis.
Getting Creutzfeldt-Jakob Disease.
Complications due to Leukocytes(white blood cells). Leukocytes often carry unwanted viruses or release toxic substances.
Complications due to recieving the wrong blood type.
Risk reduction:
All donors are given a questionnaire to determine if they have encountered any risk of getting HIV, AIDS or Hepatitis, or any other condition that would make their blood undesireable. Whether or not they are allowed to give blood is based on the questionnaire. The questionnaire MUST be completed with complete honesty.
(I believe the law can punish those who knowingly falsify the questionaire, since it can lead to death in extreme cases.)
All blood donors have their blood type determined, and their blood goes through several screening tests for disease and cell counts before it is given to anyone. If a disease is present, the donor is notified.
Blood can be, and often is filtered to reduce the number of leukocytes which are the main risk factor.
Recieving blood from a family member reduces risk of volunteer donated blood transfusions, since it is more genetically similar to your blood. (Family members are screened just as rigourously as non-family members.)
Hospitals always give persons with unknown blood type type O blood, which is the universal donor.
Reference: http://www.bloodtransfusion.com/