Essay
Critically review the laboratory tests used to diagnose iron deficiency
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Essay of 2 pages for the course laboratory investigation of disease at LJMU (essay prep for exam)
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Critically review the laboratory tests used to diagnose iron deficiency.Iron deficiency is defined as the decrease of the total iron content in the body. Anaemia due
to iron deficiency occurs when the ID is severe enough to reduce erythropoiesis. Iron
deficiency is most commonly caused by excessive loss of iron but in some cases, through a
decreased iron absorption. The daily intake of iron in the diet compensates for the amount
lost in sweat, tears, blood loss and faeces. This balance can be easily broken due to
limitations in oral absorption of iron.
Iron deficiency is a relatively common condition worldwide. In the developing world, ID is
caused due to a lack of iron intake and/or parasitic infection being the major causes. In the
developed world however, those who choose a vegetarian/vegan diet are at risk of ID as well
as those who have insufficient iron absorption and chronic blood loss. Those at increased
risk of ID are children and adolescents due to expanding erythropoiesis during periods of
rapid growth. Women of child-bearing age are at increased risk during periods of excessive
blood loss. In postmenopausal women and adult males the most common causes are likely
to be digestive diseases. This data needs to be used in conjunction with a detailed clinical
history in order to plan a diagnostic strategy for each case.
The first stage of ID diagnosis is the evaluation of the clinical presentations in combination
with a detailed patient history. Some patients can present asymptomatically but the majority
of patients show varying degrees of weakness, fatigue, irritability, headaches and lack of
concentration. In some cases of iron deficiency, pica is seen. Pica is a psychological
condition characterised by an increased appetite for substances that are deemed non-
nutritious. The most common pica seen with ID is pagophagia. Symptoms that are indicative
of a gastrointestinal malignancy should be noted i.e. abdominal pain, any change in bowel
movements, weight loss and dysphagia. A family history of any GI disorders, haematological
disorders and bleeding disorders should also be noted.
Physical examination results often show pallor (an unhealthy pale appearance), cheilosis
(painful inflammation and cracking of the corners of the mouth) and atrophic glossitis
(appearance of the characteristic glossy tongue that is tender and painful due to complete
atrophy of the lingual papillae). Urine testing for microscopic haematuria and a rectal
examination should be included the physical examination.
The laboratory diagnosis of iron deficiency is well established, except in cases of chronic
infection and inflammation. The increased number of cytokines and hepcidin levels casue
the maldistribution of iron across the body and confounds the diagnostic parameters. One of
the first laboratory investigations performed is a full blood count. The results will show
microcytosis (reduced mean cell volume), hypochromia (reduced mean cell haemoglobin)
and an increased red cell distribution width. An increased red cell width is a common finding,
particularly in the early stages of deficiency when newly produced small hypochromic red
cells coexist with normal red cells.
The presence of microcytosis does not necessarily indicate iron deficiency as the cause of
this is a common occurrence in other anaemias. The mean cell haemoglobin result is also
not sensitive or specific enough to diagnose iron deficiency. The haemoglobin level is
required to exclude anaemia. Iron deficiency without anaemia shows normal haemoglobin
levels i.e. within reference ranges (males 130-180 g/L and females 115-165g/L). Iron
deficiency with anaemia shows haemoglobin levels below these reference ranges.
Interpretation of iron metabolism results is the next stage in the diagnosis of iron deficiency.
Serum ferritin has become one of the most preferred biochemical tests as it has the greatest
specificity and sensitivity to identify ID. This test reflects the patients iron stores. Serum
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