BLOOD LEVEL
BLOOD TESTS
A 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 level
The concentration of a given
substance in the blood plasma or serum
that may be measured by
blood tests.
blood poisoning
A common name for
septicaemia
with
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 shock
may be caused by toxins
released by bacteria. Treatment is with
antibiotic drugs
and intensive therapy
for shock. (See also
bacteraemia.)
blood pressure
The 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
sphygmomanometer
and 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 80mmHg dias-
tolic). Abnormally high blood pressure
is called
hypertension
; abnormally low
pressure is termed
hypotension
.
blood products
Donated 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 o f
the newborn.
Washed red cells (with
white blood cells and/or plasma pro-
teins removed) are used when a person
needs repeated transfusions because
there is less risk of an
allergy
to 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 disorder
because 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 syndrome
and
chronic liver disease.
Concentrates of blood clotting factors
VIII and IX are used in the treatment
of
haemophilia
and
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 smear
See
blood film.
blood sugar
See
blood glucose.
blood tests
Analysis 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 count
and
blood group
tests 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, as
B
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