Transferrin (Blood)

Diagnostic Use

Transferrin is the predominant transport protein for iron in blood, responsible for most of the total iron binding capacity. It is normally about one third saturated with iron.

Raised transferrin can be seen in
– Iron deficiency (may not be elevated if associated with inflammation or severe protein malnutrition)
– Pregnancy (can be 1.7x above non-pregnant level at term)
– Oral contraceptives / Estrogen administration

Reduced transferrin can be seen in
– Inflammation or malignancy (as negative acute phase reactant)
– Protein losing state e.g. nephrotic syndrome or protein losing enteropathy
– Protein malnutrition
– Hereditary atransferrinaemia

Transferrin can be raised in early acute hepatitis and it can be reduced in chronic liver disease. Transferrin are usually normal or slightly reduced in hereditary haemochromatosis or thalassemia trait.

Interpretation

Transferrin saturation is derived from plasma iron divided by estimated total iron binding capacity. This estimated total iron binding capacity is calculated from measured transferrin multiplied by a fixed factor based on a few assumptions. For most practical purposes, this estimated total iron binding capacity closely matches the traditional measured total iron binding capacity thus the derived Transferrin saturation is very similar to Iron saturation.

However, when iron saturation becomes >50% (e.g. in hereditary haemochromatosis), contribution of iron binding by other plasma proteins e.g. albumin becomes more significant. Thus, one cannot accurately calculate transferrin from total iron binding capacity or vice versa by using a fixed factor across the whole range of iron saturation.

Another calculated index, the Transferrin Index can also be used to assist diagnosis of iron overload or iron deficiency. Unlike transferrin saturation, it has the advantage of not having assumption in its calculation. The index is simply dividing plasma Fe (in umol/L) by [ Transferrin (in g/L) x 12.57 ]. Transferrin index normally ranged between 0.33-0.43. Transferrin index >1.0 is suggestive of iron overload. Transferrin index <0.2 is suggestive of iron deficiency. Transferrin index ≤0.17 can also be used to distinguish iron deficiency anaemia from heterozygous beta-thalassemia trait.

Reference Intervals