G6PD deficiency) may result in episodes
of haemolytic anaemia since the red
cells are prone to damage by infectious
illness or certain drugs or foods.
Haemolytic anaemias due to defects
outside the red cells fall into 3 main
groups. First are disorders in which red
cells are destroyed by buffeting (by arti-
ficial surfaces such as replacement heart
valves, abnormal blood-vessel linings, or
a blood clotin a vessel, for example). In
the 2nd group, the red cells are des-
troyed by the immune system. Immune
haemolytic anaemias may occur if for-
eign blood cellsenter the bloodstream,
as occurs in an incompatible blood
transfusion, or they may be due to an
autoimmune disorder. In haemolytic dis-
ease of the newborn, the baby’s red cells
are destroyed by the mother’s antibodies
crossing the placenta. Thirdly, the red
cells may be destroyed by microorgan-
isms; the most common cause is malaria.
People with haemolytic anaemia may
have symptoms common to all types of
anaemia, such as fatigue and breathless-
ness, or symptoms specifically due to
haemolysis, such as jaundice.
Diagnosis is made by examination of
the blood (see blood film). Some inher-
ited anaemias can be controlled by
removing the spleen (see splenectomy).
Others, such as G6PD deficiency, can
be prevented by avoiding the drugs
or foods that precipitate haemolysis.
Anaemias due to immune processes
can often be controlled by immunosup-
pressant drugs. Transfusions of red cells
are sometimes needed for emergency
treatment of life-threatening anaemia.
anaemia, iron-deficiencyThe most
common form of anaemiacaused by a
deficiency of iron, an essential constit-
uent of haemoglobin. The main cause of
iron-deficiency anaemia is iron loss due
to heavy or persistent bleeding; the most
common cause in women of childbear-
ing age is menstruation. Other causes
include blood loss from the digestive
tract due to disorders such as erosive
gastritis, peptic ulcer, stomach cancer,
inflammatory bowel disease, haemor-
rhoids, and bowel tumours (see colon,
cancer of). Prolonged use of aspirin
and other nonsteroidal anti-inflammatorydrugs (NSAIDs) can cause gastrointes-
tinal bleeding. In some countries, hook-
worm infestationof the digestive tract is
an important cause of anaemia. Rarely,
bleeding may also occur as a result of
disorders of the urinary tract (such as
kidney tumours or bladder tumours).
Iron deficiency may also be caused or
worsened by lack of iron in, or its poor
absorption from, the diet.
The symptoms are those of the under-
lying cause, along with a sore mouth or
tongue, and those common to all forms
of anaemia, such as fatigue and breath-
lessness. The diagnosis is made from
blood tests and tests to look for an
underlying cause. Treatment is given for
the cause, along with a course of iron
tablets or, very rarely, injections.
anaemia, megaloblasticAn important
type of anaemiacaused by a deficiency
of vitamin B 12 or another vitamin, folic
acid. Either of these deficiencies seri-
ously interferes with production of red
blood cells in the bone marrow. An
excess of cells called megaloblasts ap-
pears in the marrow. Megaloblasts give
rise to enlarged and deformed red
blood cells known as macrocytes.
Vitamin B 12 is found only in foods of
animal origin, such as meat and dairy
products. It is absorbed from the small
intestine after first combining with
intrinsic factor, a chemical produced by
the stomach lining. The most common
cause of vitamin B 12 deficiency is failure
of the stomach lining to produce intrin-
sic factor, usually due to an autoimmune
disorder; this is called pernicious anae-
mia. Total gastrectomy(removal of the
stomach) prevents production of intrin-
sic factor, and removal of part of the
small intestine prevents B 12 absorption,
as does the intestinal disorder Crohn’s
disease. In a minority of cases, vitamin
B 12 deficiency is due to a vegan diet.
Folic acid is found mainly in green
vegetables and liver. The usual cause of
deficiency is a poor diet. Deficiency can
also be caused by anything that inter-
feres with the absorption of folic acid
from the small intestine (for example
Crohn’s disease or coeliac disease). Folic
acid requirements are greater than nor-
mal in pregnancy.ANAEMIA, IRON-DEFICIENCY ANAEMIA, MEGALOBLASTICA