Bma Illustrated Medical Dictionary

blood countA test, also called full

blood count, that measures haemoglo-

binconcentration and the numbers of

red blood cells, white blood cells, and

platelets in 1 cu. mm of blood. The pro-

portion of various white blood cells is

measured and the size and shape of red

and white cells is noted. It is the most

commonly performed blood test and is

important for diagnosing anaemiaor

confirming the presence of an infection

to which the blood has responded. It is

also used to diagnose disorders such as

leukaemiaand thrombocytopenia.

blood cultureSee culture.

blood, disorders ofDisorders result-

ing from abnormalities in any of the

components of blood or from infection.

Disorders include types of anaemia,

polycythaemia, bleeding disorders,and

unwanted clot formation (thrombosis),

hypoalbuminaemia (albumindeficiency)

and agammaglobulinaemia (deficiency

of gamma-globulin). Blood disorders

such as sickle cell anaemia, thalassaemia,

and haemophilia are inherited. Bone

marrow cancers that affect production

of blood components include leukaemia,

polycythaemia vera, and multiple myelo-

ma. Blood poisoning is usually due to

septicaemiaor a toxin such as carbon

monoxide. Some drugs can cause blood

abnormalities as a side effect. (See also

anaemia,haemolytic; anaemia,iron-defi-

ciency; anaemia,megaloblastic; malaria;

hyperbilirubinaemia.)

blood donationThe process of giving

blood for use in blood transfusion.

series of chemical reactions that lead to
the formation of a clot to seal the
injury. First, plateletsaround the injury
site are activated, becoming sticky and
adhering to the blood-vessel wall. Then,
the activated platelets release chemi-
cals, which, in turn, activate blood
clotting factors. These factors, together
with vitamin K, act on fibrinogenand
convert it to fibrin. Strands of fibrin
form a meshwork, which traps red blood
cells to form a clot.
There are several anticlotting mecha-
nisms to prevent the formation of
unwanted clots. These include prosta-
cyclin (a prostaglandin), which prevents
platelet aggregation, and plasmin, which
breaks down fibrin (see fibrinolysis).
Blood flow washes away active coagula-
tion factors; and the liver deactivates
excess coagulation factors.
Defects in blood clotting may result in
bleeding disorders. Excessive clotting
(thrombosis) may be due to an inherited
increase or defect in a coagulation factor
(see factor V), the use of oral contracep-
tives, a decrease in the level of enzymes
that inhibit coagulation, or sluggish
blood flow through a particular area.
Treatment is usually with anticoagulant
drugssuch as heparin or warfarin.
blood-clotting testsTests to screen
for and diagnose bleeding disorders,
usually resulting from deficiencies or
abnormalities of blood coagulation fac-
tors or of platelets (see blood clotting).
Tests are also used to monitor treat-
ment with anticoagulant drugs.

BLOOD CLOTTING

BLOOD-CLOTTING TESTS BLOOD DONATION

Site of B
injury

Red blood

cell

PLATELETS ACTIVATED BLOOD CLOT FORMS

Blood vessel

Platelet constricts

Trapped red

blood cell

Fibrin

Platelet meshwork