Serum Transferrin Receptor to Ferritin Index

 

Tissue transferrin receptor is a transmembrane protein with 2 identical polypeptide chains that helps transport iron into cells. The soluble receptor is a monomer truncated from the tissue receptor. It forms a complex with ferritin that circulates within the blood. The level of circulating transferrin receptor is proportional to the tissue transferrin receptor level.

 

The level of tissue and serum transferrin receptor tends to change opposite to the body iron stores.

(1) As the body iron stores decline, the transferrin receptor levels increase.

(2) As the body iron stores increase, as in hemochromatosis, the transferrin receptor levels decrease.

 

serum (soluble) transferrin receptor to ferritin index =

= (serum transferrin receptor in mg/L) / LOG10 (serum ferritin in µg/L)

 

NOTE: In all of the papers reviewed, I could not find a specification for the logarithm as base 10 or natural logarithm. Based on trial and error approximations of the tabular data, LOG10 appears the more appropriate.

 

In the data given by Suominen et al (Figure 1, page 2935):

State	Serum Ferritin	Serum Transferrin Receptor	Transferrin Receptor to Ferritin Index
normal iron levels	22 – 203 µg/L	1.15 – 2.75 mg/L	0.63 – 1.8
depletion of iron stores	< 22 µg/L	<= 2.75 mg/L	> 1.8
depletion of functional iron	< 22 µg/L	> 2.75 mg/L	> 2.2
iron deficiency anemia	< 22 µg/L	> 3.6 mg/L	> 2.8

 

Limitations:

• The cutoff points need to be determined by each laboratory.