donations the same as general donations, many
health experts are concerned that donors may not
be forthcoming during the health screening
process, raising the risk for the blood to carry
pathogens. The tests blood banks run on each unit
of donated blood may not detect the presence of
certain infections, making accurate health screen-
ing essential.
See also BONE MARROW DONATION; CREUTZFELDT-
JAKOB DISEASE (CJD); HEMOCHROMATOSIS; HEMAPHERE-
SIS.
blood stem cells The parent cells from which all
BLOODcells arise. Blood stem cells are pluripotent
or undifferentiated, which means they have the
ability to become any of the three types of blood
cells (erythrocytes, leukocytes, or platelets). Intri-
cate biochemical interactions determine how the
blood stem cell will differentiate (become a spe-
cific type of blood cell). Blood stem cells reside pri-
marily in the BONE MARROWand the LY M P Htissues
though some circulate in the blood.
Blood stem cell transplantation, with harvest-
ing through BONE MARROW DONATIONand peripheral
blood stem cell (PBSC) donation, has become a
cornerstone of treatment for cancers involving the
bone marrow and blood, notably leukemias and
lymphomas. Researchers are exploring ways to
use blood stem cells in other ways. Unlike embry-
onic stem cells, which are omnipotent (can differ-
entiate into any kind of cell), blood stem cells
have limited capability to differentiate only into
the various types of blood cells. However, the
abundance and ease of collection of blood stem
cells, which can be extracted from the blood, gives
researchers hope that they may discover methods
to manipulate blood stem cell differentiation to
give rise to other kinds of cells.
See also BONE MARROW TRANSPLANTATION; CELL
STRUCTURE AND FUNCTION; HEMATOPOIESIS.
blood transfusion A therapeutic procedure to
administer BLOODor blood products. Blood trans-
fusions may be autologous (self-donated), when
the timing of the need for blood permits planning,
or allogeneic (volunteer donor). The transfusion
of blood or blood products takes place intra-
venously, through a sterile needle inserted into a
VEIN. Receiving a transfusion may take 10 to 20
minutes, depending on the blood product, condi-
tion of the recipient’s veins, and the urgency with
which the person needs the blood product. Frozen
blood products are thawed, and most blood prod-
ucts are brought to body temperature, before
administration.BLOOD RECLAMATION DURING SURGERY
Many hospitals use BLOOD reclamation, also
called blood collection, procedures to collect,
cleanse, and return to the person during the
OPERATIONblood lost during a major surgery such
as orthopedic, transplant, or OPEN HEART SURGERY.
This practice reduces the need for blood transfu-
sions.Blood Type Compatibility
Though physicians attempted blood transfusions
as early as the 17th century, many hazards and
failures accompanied the procedure until
researchers discovered blood types in the early
1900s. The techniques to allow consistent detec-
tion of BLOOD TYPE, called type and cross-match,
finally became available in the 1950s. Doctors
then were able to routinely match the blood type
and rhesus (Rh) factor of donors to recipients and
blood transfusions became a standard element of
medical care. Transfusion of whole blood and cell-
containing blood products such as red blood cells
(erythrocytes) requires blood type compatibility
between donor and recipient; transfusion of other
blood products such as PLASMA, ALBUMIN, and CLOT-
TING FACTORSdoes not.BLOOD PRODUCTS FOR TRANSFUSION
whole BLOOD packed red blood cells
PLASMA ALBUMIN
clotting factor VII clotting factor IX
platelets cryoprecipitated antihemophilic
fibrinogen factor (AHF)
antithrombin III anti-inhibitor coagulation
IMMUNOGLOBULIN complex (AICC)
Rh immunoglobulin alpha 1-proteinase inhibitor
granulocytesTransfusion Reaction
Blood type incompatibility, though uncommon in
transfusion, can lead to reactions spanning the
spectrum from mild to fatal. Comprehensive typeblood transfusion 129