Other investigations of iron metabolism
These are not usually required to diagnose iron-deficiency anaemia but are available from most
laboratories and can support the diagnosis. Below is a list of the more common investigations.
Serum iron
Serum iron only measures a fraction of the iron in the blood. It can only measure the ferric
form (Fe3+) and not the iron incorporated in haemoglobin molecules.
Serum iron levels show diurnal variation and are sensitive to recent iron intake therefore,
measuring serum iron in isolation has no role in determining a patient’s iron stores.
Total iron-binding capacity (TIBC)
The TIBC is calculated by taking a serum sample and adding excess iron to fully saturate the
iron carrying molecules.
The TIBC is a measurement of the total iron concentration in the sample when fully saturated.
TIBC can rise in an iron-deficient state, but specificity is poor. Hence, BSH does not
recommend routinely using this to assess iron stores.
Transferrin
Transferrin is the main serum iron transporter molecule which can be measured in a patient’s
serum.
Like TIBC, transferrin can rise in iron deficiency as the body tries to increase the total iron-
binding capacity. However, transferrin is a negative acute-phase protein and so decreases in
inflammatory states.
Soluble transferrin receptor (STFR)
Transferrin receptors are present on developing red cells and can be detected in their soluble
form in peripheral blood.
In iron deficiency, these developing cells display an increased number of transferrin
receptors as they try to acquire more iron, this increase can be measured in the serum.
Unlike ferritin, this is not affected by inflammation and so can be helpful in distinguishing
anaemia of chronic disease from iron deficiency anaemia.
A rise in STFR is not specific to iron deficiency with other potential causes including
haemolysis, thalassaemia, megaloblastic anaemia, and hypoxia. STFR can also be normal in
mild deficiency, only becoming abnormal in more advanced stages.
Due to the lack of specificity and comparatively high cost, BSH does not recommend
measuring STFR when investigating iron deficiency.
These are not usually required to diagnose iron-deficiency anaemia but are available from most
laboratories and can support the diagnosis. Below is a list of the more common investigations.
Serum iron
Serum iron only measures a fraction of the iron in the blood. It can only measure the ferric
form (Fe3+) and not the iron incorporated in haemoglobin molecules.
Serum iron levels show diurnal variation and are sensitive to recent iron intake therefore,
measuring serum iron in isolation has no role in determining a patient’s iron stores.
Total iron-binding capacity (TIBC)
The TIBC is calculated by taking a serum sample and adding excess iron to fully saturate the
iron carrying molecules.
The TIBC is a measurement of the total iron concentration in the sample when fully saturated.
TIBC can rise in an iron-deficient state, but specificity is poor. Hence, BSH does not
recommend routinely using this to assess iron stores.
Transferrin
Transferrin is the main serum iron transporter molecule which can be measured in a patient’s
serum.
Like TIBC, transferrin can rise in iron deficiency as the body tries to increase the total iron-
binding capacity. However, transferrin is a negative acute-phase protein and so decreases in
inflammatory states.
Soluble transferrin receptor (STFR)
Transferrin receptors are present on developing red cells and can be detected in their soluble
form in peripheral blood.
In iron deficiency, these developing cells display an increased number of transferrin
receptors as they try to acquire more iron, this increase can be measured in the serum.
Unlike ferritin, this is not affected by inflammation and so can be helpful in distinguishing
anaemia of chronic disease from iron deficiency anaemia.
A rise in STFR is not specific to iron deficiency with other potential causes including
haemolysis, thalassaemia, megaloblastic anaemia, and hypoxia. STFR can also be normal in
mild deficiency, only becoming abnormal in more advanced stages.
Due to the lack of specificity and comparatively high cost, BSH does not recommend
measuring STFR when investigating iron deficiency.
