Transferrin Receptor

Transferrin receptors, which are blood proteins, may be elevated in persons with iron deficiency. Transferrin receptor testing is used to measure the level of soluble transferrin receptors, thereby aiding in the evaluation of iron deficiency and in the diagnosis of iron-deficiency anemia.

The reference range of transferrin receptor varies by sex in adults.

Normal findings ^[1] :

• Men: 2-5 mg/L
• Women: 1.9-4.4 mg/L

Result variations are engendered by the testing method. 

Transferrin receptor levels within the reference range indicate normal physiology.

Elevated levels are seen in iron-deficiency anemia.

Decreased transferrin receptor levels are seen in the following:

• Iron overload

• Protein malnutrition

• Atransferrinemia (genetic absence of transferrin receptor)

Collection: Serum separator tube or plasma separator tube; green (sodium or lithium heparin), lavender (EDTA), or pink (K₂ EDTA) tubes are also acceptable

Specimen preparation: Transfer 1 mL (minimum, 0.3 mL) of serum or plasma to a tube

Storage/transport temperature: Refrigerated

Unacceptable conditions: Contaminated, severely hemolyzed, icteric, or lipemic specimens

Stability after separation from cells (collection to initiation of testing): ambient, 72 hours; refrigerated, 1 week; frozen, 1 month (avoid repeated freeze/thaw cycles) ^[2]

Definition

Transferrin receptors, which are blood proteins, may be elevated in persons with iron deficiency. Transferrin receptor testing is used to measure the level soluble transferrin receptors, thereby aiding in the evaluation of iron deficiency and in the diagnosis of iron-deficiency anemia.

Transferrin is an iron-binding glycoprotein found in the plasma. Its main function is to control the level of free iron. ^[3] Unlike ferritin, the transferrin receptor level is not affected by infection or inflammation and is therefore useful in distinguishing iron deficiency anemia from anemia of chronic disease. ^[4]

Indications/Applications

Transferrin receptor testing is used in the diagnosis of anemia and in deciding adequate treatment. Along with other tests in an anemia panel (iron, ferritin, reticulocyte count, lactate dehydrogenase [LDH], vitamin B-12, folate), the type of anemia can be diagnosed based on the transferrin receptor levels.

Transferrin receptor testing is particularly useful in the evaluation of microcytic anemia (with mean corpuscular volume [MCV] < 75) to distinguish iron-deficiency anemia from anemia of chronic disease from anemia of chronic inflammation.

Considerations

Table 1. Anemia Tests (Open Table in a new window)

A study by Sierpinski et al indicated that in patients with heart failure, serum soluble transferrin receptor is a better biomarker than serum ferritin or transferrin saturation for predicting iron deficiency in bone marrow. Using a cutoff value of 1.25 mg/L, the receptor had a sensitivity and specificity of 84% and 100%, respectively, for diagnosing such deficiency. Iron deficiency is associated with poor prognosis in heart failure, with the investigators reporting that for soluble transferrin receptors, a level of 1.41 mg/L or greater was “the optimal threshold for predicting 3-year mortality” in the study’s patients, “independent of other established variables.” Patients had ischemic heart failure and a left ventricular ejection fraction of 45% or less. ^[5]

Similarly, a study by Fitzsimons et al found a link between iron deficiency as manifested in a soluble transferrin receptor level of 1.76 mg/L or greater and all-cause mortality in persons with heart failure and preserved ejection fraction, the hazard ratio for that receptor level being 1.84. ^[6]