Anaemia is the general name for a range of
disorders affecting red blood cells. Red blood
cells contain haemoglobin, which is responsible
for carrying oxygen in the blood. To produce
red blood cells, the body needs, iron, vitamin
B12 and folic acid. If one or more of these
is deficient, anaemia will develop. Red blood
cells are produced in the bone marrow and
circulate in the bloodstream before they are
broken down in the spleen. If the level of
red cells (and therefore of haemoglobin),
in the blood is abnormally low the oxygen-carrying
capacity of blood is reduced and anaemia develops.
Haemoglobin is measured in terms of the weight
present in grams (g) per 100 millilitres (1
decilitre or dl) of blood. A normal level
in females will lie somewhere between 11.5
and 15.5 g per dl, and in males between 13
and 18 g per dl. The normal range of red cell
numbers per cubic millimetre of blood is 4,100,000–5,200,000
in females and 4,400,000–5,800,000 in
males. Iron
deficiency anaemia is the most common type
of anaemia. It affects up to 30% of the
world’s population. Up to 14% of menstruating
women in developed countries have iron deficiency
anaemia. Megaloblastic anaemia (the red
cells are megablastic i.e. large and abnormal)
develops if vitamin B12 or folic acid are
lacking. A lack of folic acid, leads to
megaloblastic anaemia. Another type of megablastic
anaemia is called ‘pernicious’
anaemia, in which there is insufficient
absorption of vitamin B12 from the diet.
Haemolytic anaemia
occurs as the result of an inherited r an
acquired condition in which the body destroys
red blood cells prematurely. Haemolysis
describes the breaking up of red blood cells,
resulting in the release of haemoglobin
into the plasma.
Aplastic anaemia results
from the failure of the bone marrow to produce
sufficient numbers of red blood cells.
Causes
Each type of anemia
has different causes: Iron-deficiency
anaemia is caused by a shortage of iron.
It affects women much more often than men,
because women lose some blood in each menstrual
period between puberty and the menopause.
An average healthy mixed diet will contain
enough iron to make up normal menstrual
losses, but unusually heavy periods, a poor
diet, or large loses of weight can lead
to a shortage of iron.
In some cases there
is also blood loss from elsewhere, especially
from the stomach/ intestine. This may be
from stomach and duodenal ulcers or from
piles. Bleeding high up in the intestine
turns the stools (faeces) black. Bleeding
piles produce visible red blood.
Chronic diseases,
such as infections, cancer and rheumatoid
arthritis, can cause iron-deficiency anaemia
because the developing red cells in the
bone marrow are unable to use the iron reserves.
Haemolytic anaemia
occurs when red blood cell destruction is
increased as the result of an acquired or
inherited condition, which generally interferes
with normal red blood cell production. They
include hereditary Spherocytosis, Sickle
cell anaemia, and Thalassaemia. ·
Megaloblastic anaemia
develops if vitamin B12 or folic acid are
lacking and is mainly caused by a diet low
in fresh fruit and vegetables. Reduced absorption
of folic acid may be due to excessive alcohol
consumption and by some medicines. There
is an increased need for folic acid during
pregnancy. Folic acid deficiency also occurs
in people with cancer and in those with
coeliac disease.
Pernicious anaemia
is caused by a shortage of vitamin B12.
This is usually because the vitamin is not
being absorbed, because the stomach lining
does not produce a certain chemical ('intrinsic
factor'). The bone marrow needs vitamin
B12 in order to produce red blood cells.
In pernicious anaemia the blood contains
a smaller number of abnormally large cells
(megablastic), which do not last as long
as normal.
In Aplastic anaemia,
the bone marrow does not make any new red
cells, nor indeed any other kind of blood
cells, and so the immune system can’t
work properly. The average life of a red
cell is 120 days, so new cells have to be
made all the time. If this does not happen,
the anaemia will get steadily worse and
create a very serious situation.
About a third of all
cases of aplastic anaemia follow virus infections,
especially measles, mumps and hepatitis,
or are caused by drugs such as butazolidine,
sulphonamides, chloramphenicol by mouth
or dipyrone. Because of this risk, most
of these drugs are no longer prescribed.
Inhaling benzene fumes can also cause aplastic
anaemia. In most cases, however, the cause
remains obscure.
The condition is rare,
affecting only 2 to 5 people per million.
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Anaemia
