BLOOD FILM
BLOOD GROUPS
Donated blood is tested for a range of
infectious agents such as
hepatitis B
and
hepatitis C
and antibodies to
HIV.
After being classified into
blood groups,
the blood is stored in a blood bank,
either whole or separated into its differ-
ent components (see
blood products).
Apheresis is a type of blood donation in
which only a specific blood component,
such as plasma, platelets, or white
cells, is withdrawn from the donor,
blood film A test that involves smear-
ing a drop of blood on to a glass slide
for examination under a microscope.
The blood film is stained with dyes to
make the blood cells show up clearly.
The test allows the shape and appear-
ance of blood cells to be checked for
any abnormality, such as the sickle-
shaped red blood cells characteristic of
sickle cell anaemia.
The relative propor-
tions of the different types of white
blood cells can also be counted. This
examination, called a differential white
cell count, may be helpful in diagnosing
infection or
leukaemia.
Blood films are
also used in diagnosing infections, such
as
malaria,
in which the parasites can
be seen inside the red blood cells.
Blood films are usually carried out
together with a full
blood count.
blood gases A test for determining the
acidity-alkalinity (pH) and the concen-
trations of oxygen, carbon dioxide, and
bicarbonate in the blood. The test is
carried out on a sample of blood taken
from an artery, usually at the wrist or
groin. It is useful in diagnosing and mon-
itoring
respiratory failure.
Bicarbonate
and acidity reflect the
acid-base balance
of the body, which may be disturbed in
conditions such as diabetic ketoacido-
sis, aspirin poisoning, hyperventilation,
or repeated vomiting. Blood oxygen can
also be measured without taking a
blood sample by using an
oximeter.
blood glucose The level of
glucose
in
the blood. Abnormally high blood glu-
cose (sometimes called sugar) levels are
an indication of
diabetes mellitus.
(See
also
h}sperglycaemia; tyspoglycaemia.)
blood groups Systems of classifying
blood according to the different marker
proteins (
antigens
) on the surface of red
blood cells and antibodies in the plas-
ma. These antigens affect the ability of
the red blood cells to provoke an
immune response.
There are 2 main
blood grouping systems: the ABO sys-
tem and the rhesus system.
In the ABO system, the presence or
absence of 2 types of antigen (named A
and B) on the surface of the red blood
cells determine whether a person's
blood group is A, B, AB (which has both
A and B), or O (which has neither A nor
B). People with the A antigen (group A)
have anti-B antibodies; people with the
B antigen (group B) have anti-A anti-
bodies; those with both antigens (blood
group AB) have neither; and those with
neither antigen (group O) have both.
The rhesus system involves several
antigens, the most important of which
is factor D. People with this factor are Rh
positive; those without it are Rh neg-
ative. The importance of the Rh group
relates mainly to pregnancy in Rh-
negative women, since, if the baby
is Rh positive, the mother may form
antibodies against the baby's blood
(see
rhesus incompatibility).
BLOOD GROUPS
BLOOD GROUPA
BLOOD GROUP B
BLOOD GROUP AB
BLOOD GROUP O
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