Iron Deficiency Anaemia

in medicine •  2 years ago 

Overview

• Iron defi ciency is the commonest cause of anaemia worldwide
• Iron defi ciency is usually easily diagnosed from the red cell indices
• A drop in haemoglobin is generally a late feature of iron defi -
ciency
• The serum ferritin is a reliable means of confi rming the diagnosis
but may be falsely normal or even elevated as a reactive phenomenon
as ferritin is an acute phase protein
• Iron defi ciency is not a diagnosis in itself and in males and postmenopasual
women blood loss from the gastrointestinal tract
must be excluded
• Oral iron is preferred for iron replacement therapy, but occasionally
parenteral iron is required

Defination: Iron defi ciency is the commonest cause of anaemia worldwide and is
frequently seen in general practice. Iron defi ciency anaemia is caused
by defective synthesis of haemoglobin, resulting in red cells that are
smaller than normal (microcytic) and contain reduced amounts of
haemoglobin (hypochromic).

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Iron metabolism:
Iron has a pivotal role in many metabolic processes, and the average
adult contains 3–5 g of iron, of which two-thirds is in the oxygencarrying
molecule haemoglobin.
A normal Western diet provides about 15·mg of iron daily, of which
5–10% is absorbed (~·1·mg), principally in the duodenum and upper
jejunum, where the acidic conditions help the absorption of iron in
the ferrous form. Absorption is helped by the presence of other reducing
substances, such as hydrochloric acid and ascorbic acid. The
body has the capacity to increase its iron absorption in the face of increased
demand, for example, in pregnancy, lactation, growth spurts
and iron defi ciency.
Once absorbed from the bowel, iron is transported across the mucosal
cell to the blood, where it is carried by the protein transferrin
to developing red cells in the bone marrow. Iron stores comprise ferritin,
a labile and readily accessible source of iron and haemosiderin,
an insoluble form found predominantly in macrophages.
About 1·mg of iron a day is shed from the body in urine, faeces,
sweat and cells shed from the skin and gastrointestinal tract. Menstrual
losses of an additional 20·mg per month and the increased
requirements of pregnancy (500–1000·mg) contribute to the higher
incidence of iron deficiency in women of reproductive age.

Clinical features of iron deficiency:
The symptoms accompanying iron defi ciency depend on how rapidly
the anaemia develops. In cases of chronic, slow blood loss, the body
adapts to the increasing anaemia and patients can often tolerate extremely
low concentrations of haemoglobin, for example, <·7.0 g/dL,
with remarkably few symptoms. Most patients complain of increasing
lethargy and dyspnoea. More unusual symptoms are headaches, tinnitus
and taste disturbance.
On examination, several skin, nail and other epithelial changes may
be seen in chronic iron defi ciency. Atrophy of the skin occurs in about
a third of patients and (rarely nowadays) nail changes such as koilonychia
may result in brittle, flattened nails. Patients may also complain of angular stomatitis, in which painful
cracks appear at the angle of the mouth, sometimes accompanied
by glossitis. Although uncommon, oesophageal and pharyngeal webs
can be a feature of iron defi ciency anaemia (consider this in middle
aged women presenting with dysphagia). These changes are believed to be due to a reduction in the iron-containing enzymes in the epithelium
and gastrointestinal tract. Few of these epithelial changes are
seen in modern practice, and they are of limited diagnostic value.
Tachycardia and cardiac failure may occur with severe anaemia
irrespective of cause and, in such cases, prompt remedial action
should be taken.
When iron defi ciency is confi rmed, a full clinical history, including
leading questions on possible gastrointestinal blood loss or malabsorption
(as in, for example, coeliac disease), should be obtained.
Menstrual losses should be assessed and the importance of dietary
factors and regular blood donation should not be overlooked.
Diet alone is seldom the sole cause of iron defi ciency anaemia in
the UK except when it prevents an adequate response to a physiological
challenge, as in pregnancy, for example.

Causes of iron defi ciency anaemia
Reproductive system
• Menorrhagia
Gastrointestinal tract
Bleeding
• Oesophagitis
• Oesophageal varices
• Hiatus hernia (ulcerated)
• Peptic ulcer
• Infl ammatory bowel disease
• Haemorrhoids (rarely)
• Carcinoma: stomach, colorectal
• Angiodysplasia
• Hereditary haemorrhagic telangiectasia (rare)
Malabsorption
• Coeliac disease
• Atrophic gastritis (also may result from iron defi ciency)
Physiological
• Growth spurts (especially in premature infants)
• Pregnancy
Dietary
• Vegans
• Elderly
• Other
• Patients with chronic renal failure undergoing haemodialysis and
receiving erythropoietin.

Laboratory investigations:
A full blood count and fi lm should be assessed. These will
confi rm the anaemia; recognizing the indices of iron defi ciency is
usually straightforward (reduced haemoglobin concentration, reduced
mean cell volume, reduced mean cell haemoglobin, reduced
mean cell haemoglobin concentration) . Some modern
analysers will determine the percentage of hypochromic red cells,
which may be high before the anaemia develops (it is worth noting
that a reduction in haemoglobin concentration is a late feature
of iron defi ciency). The blood fi lm shows microcytic hypochromic
red cells . Hypochromic anaemia occurs in other disorders,
such as anaemia of chronic disorders and sideroblastic anaemias, and in globin synthesis disorders, such as thalassaemia.
To help to differentiate the type, further haematinic assays may be
necessary. Historically, serum iron and total iron binding capacity
(TIBC) were used in the diagnosis of iron defi ciency anaemia, but
because of the wide diurnal variation seen in iron levels and the
lack of sensitivity, these assays are seldom used today. Diffi culties in
diagnosis arise when more than one type of anaemia is present, for
example, iron defi ciency and folate defi ciency in malabsorption, in
a population where thalassaemia is present, or in pregnancy, when
the interpretation of red cell indices may be diffi cult.
Haematinic assays will demonstrate reduced serum ferritin concentration
in straightforward iron defi ciency. As an acute phase protein,
however, the serum ferritin concentration may be normal or
even raised in inflammatory or malignant disease. A prime example of this is found in rheumatoid disease, in which
active disease may result in a spuriously raised serum ferritin concentration
masking an underlying iron deficiency caused by gastrointestinal
bleeding after non-steroidal analgesic treatment. There may also
be confusion in liver disease, as the liver contains stores of ferritin
that are released after hepatocellular damage, leading to raised serum
ferritin concentrations. In cases where ferritin estimation is likely to
be misleading, the soluble transferrin receptor (sTfR) assay may aid
the diagnosis.
Transferrin receptors are found on the surface of red cells in greater
numbers in iron defi ciency; a proportion of receptors is shed into the
plasma and can be measured using commercial kits. Unlike serum
ferritin, the level of sTfR does not rise in inflammatory disorders, and hence can help to differentiate between anaemia due to infl ammation
and iron defi ciency.
Diagnostic bone marrow sampling is seldom performed in simple
iron defi ciency, but, if the diagnosis is in doubt, a marrow aspirate
may be carried out to demonstrate absent bone marrow stores.
When iron deficiency has been diagnosed, the underlying cause
should be investigated and treated. Often the history will indicate
the likely source of bleeding, for example, menstrual blood loss or
gastrointestinal bleeding. If there is no obvious cause, further investigation
generally depends on the age and sex of the patient. In
male patients and postmenopausal women, possible gastrointestinal
blood loss is investigated by visualization of the gastrointestinal
tract (endoscopic or barium studies). Faecal occult blood tests are of
no value in the investigation of iron deficiency.

Management:

Effective management of iron defi ciency relies on (i) the appropriate
management of the underlying cause (for example, gastrointestinal
or menstrual blood loss) and (ii) iron replacement therapy.
Oral iron replacement therapy, with gradual replenishment of iron
stores and restoration of haemoglobin, is the preferred treatment.
Oral ferrous salts are the treatment of choice (ferric salts are less well
absorbed) and usually take the form of ferrous sulphate 200·mg three
times daily (providing 65 mg·×·3·= 195·mg elemental iron/day). Alternative preparations include ferrous gluconate and ferrous fumarate. All three compounds, however, are associated
with a high incidence of side effects, including nausea, constipation
and diarrhoea. These side effects may be reduced by taking the tablets
after meals, but even milder symptoms account for poor compliance
with oral iron supplementation. It is worth noting that these lower
gastrointestinal symptoms are not dose related. Modifi ed release
preparations have been developed to reduce side effects, but in practice
prove expensive and often release the iron beyond the sites of
optimal absorption.
Effective iron replacement therapy should result in a rise in haemoglobin
concentration of around 0.1·g/dL per day (about 2·g/dL
every 3·weeks), but this varies from patient to patient. Once the haemoglobin
concentration is within the normal range, iron replacement
should continue for 3·months to replenish the iron stores.

Failure to respond to oral iron therapy:
The main reason for failure to respond to oral iron therapy is poor
compliance. However, if the losses (for example, bleeding) exceed
the amount of iron absorbed daily, the haemoglobin concentration
will not rise as expected; this will also be the case in combined defi
ciency states.
The presence of underlying infl ammation or malignancy may
also lead to a poor response to therapy. Occasionally, malabsorption
of iron, such as that seen in coeliac disease, may lead to a failure to
respond. Finally, an incorrect diagnosis of iron defi ciency anaemia
should be considered in patients who fail to respond adequately to
iron replacement therapy.

Intravenous and intramuscular iron preparations:
Parenteral iron may be used when the patient cannot tolerate oral
supplements, for example, when patients have severe gastrointestinal
side effects or if the losses exceed the daily amount that can be absorbed
orally . The rise in haemoglobin concentration is no
faster with parenteral iron preparations than with oral iron therapy.
Intramuscular iron sorbitol (a complex of iron, sorbitol and citric
acid) injection was used as a parenteral iron replacement for many
years, but was discontinued in the UK in 2003. Generally, around
10–20 deep intramuscular injections were given over 2–3·weeks.
However, side effects were common and included pain, skin staining
at the site of injection and arthralgia. Newer intravenous iron
preparations include iron hydroxide sucrose (Venofer®) and iron
dextran (Cosmofer ®, may also be given IM) for use in selected cases
and under strict medical supervision, for example, on a haematology
day unit (risk of anaphylaxis or other reactions).

Alternative treatments:
Blood transfusion is not indicated unless the patient has decompensated
due to a drop in haemoglobin concentration and needs a more
rapid rise in haemoglobin, for example, in cases of worsening angina
or severe coexisting pulmonary disease. In cases of iron defi ciency with
serious ongoing acute bleeding, blood transfusion may be required.

Prevention:
When absorption from the diet is likely to be matched or exceeded
by losses, extra sources of iron should be considered, for example, prophylactic iron supplements in pregnancy or after gastrectomy,
or encouragement of breastfeeding or use of formula milk during
the fi rst year of life (rather than cows’ milk, which is a poor source
of iron).

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