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, as follows:
Men: 2.2-5 mg/L
Women: 1.9-4.4 mg/L
Reference intervals of transferrin receptors have not been established for pregnant females, children, or recent or frequent blood donors. 
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:
Atransferrinemia (genetic absence of transferrin receptor)
Collection and Panels
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) 
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.  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. 
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.
Table 1. Anemia Tests (Open Table in a new window)
|Test||level in Iron Deficiency Anemia||level in Anemia of Chronic Disease||level in Mixed Iron Deficiency Anemia and Anemia of Chronic Disease|
|Ferritin||Low||High||Normal or high|
|Total iron-binding capacity||High||Low||Normal or high|