white blood cells and/or plasma pro-
teins removed) are used when a person
needs repeated transfusions because
there is less risk of an allergyto any of
the blood components developing.
Platelets may be given in transfusions
for people with blood-clotting disor-
ders. Patients who have life-threatening
infections may be treated with granulo-
cytes, a type of white blood cell. Fresh
frozen plasma is used to correct many
types of bleeding disorderbecause it
contains all the clotting factors. Albu-
min, prepared from the plasma of whole
blood, is used mainly to treat shock
resulting from severe blood loss until
compatible whole blood becomes avail-
able. Purified albumin preparations are
used to treat nephrotic syndromeand
chronic liver disease.
Concentrates of blood clotting factors
VIII and IX are used in the treatment
of haemophiliaand Christmas disease.
Immunoglobulins(also called antibod-
ies), which are extracted from blood
plasma, can be given by injection (see
immunoglobulin injection) to protect
people who are unable to produce their
own antibodies or have already been
exposed to an infectious agent, or to
provide short-term protection against
hepatitis A. Immunoglobulins are given
in large doses to treat certain autoim-
mune disorders.
blood smearSee blood film.
blood sugarSee blood glucose.
blood testsAnalysis of a sample of
blood to give information on its cells
and proteins and any of the chemicals,
antigens, antibodies, and gases that it
carries. Such tests can be used to check
on the health of major organs, as well
as on respiratory function, hormonal
balance, the immune system, and metab-
olism. Blood tests may look at numbers,
shape, size, and appearance of blood
cells and assess the function of clotting
factors. The most important tests are
blood countand blood grouptests if
transfusion is needed. Biochemical
tests measure chemicals in the blood
(see acid–base balance; kidney function
tests; liver function tests). Microbiologi-
cal tests (see immunoassay) look for
microorganisms that are in the blood, asA person’s blood group is inherited and
may be used in paternity testing. Gen-
etic analysis allows identification of the
blood of a criminal suspect with virtual
certainty (see genetic fingerprinting).
blood levelThe concentration of a given
substance in the blood plasma or serum
that may be measured by blood tests.
blood poisoningA common name for
septicaemiawith toxaemia, a life-threat-
ening illness caused by multiplication
of bacteria and formation of toxins in
the bloodstream. Septicaemia may be a
complication of an infection in an organ
or tissue. In some infective conditions,
septic shockmay be caused by toxins
released by bacteria. Treatment is with
antibiotic drugs and intensive therapy
for shock. (See also bacteraemia.)
blood pressureThe pressure exerted
by the flow of blood through the main
arteries. The pressure at 2 different
phases is measured. Systolic, the higher
pressure, is created by the contraction
of the heart. Diastolic, the lower, is rec-
orded during relaxation of the ventricles
between heartbeats; it reflects the resis-
tance of all the small arteries in the body
and the load against which the heart
must work. The pressure wave that is
transmitted along the arteries with each
heartbeat is easily felt as the pulse.
Blood pressure is measured using a
sphygmomanometerand is expressed
as millimetres of mercury (mmHg).
Blood pressure varies with age, between
individuals, and at different times in the
same individual but a healthy young
adult usually has a blood pressure
reading, at rest, of about 120/80 (that is
120 mmHg systolic and 80 mmHgdias-
tolic). Abnormally high blood pressure
is called hypertension; abnormally low
pressure is termed hypotension.
blood productsDonated blood that is
separated into its various components:
red cells, white cells, platelets, and
plasma (see blood donation). Each
blood product has a specific lifespan
and use in blood transfusion. Packed red
cells (blood with most of the plasma
removed) are used to treat patients
with some forms of chronic anaemia
and babies with haemolytic disease of
the newborn. Washed red cells (with
BLOOD LEVEL BLOOD TESTS
B