Soluble transferrin receptor - plasma or serum

5 mL blood in a lithium heparin or plain tube.

Varies with method, age, gender, and pregnancy.

Membrane-bound transferrin receptor is released externally during endocytosis.
Soluble transferrin receptor levels in plasma are elevated if there is increased iron demand due to iron deficiency, increased erythropoiesis (eg, haemolysis) or dyserythropoiesis (eg, megaloblastic anaemia), regardless of other, coexistent states.
Thus, it can be used to demonstrate iron deficiency in patients who also have an Acute phase response and it can distinguish Iron deficiency from the Anaemia of chronic disease.
Patients with an acute phase response have reduced plasma iron and transferrin with elevation of ferritin, making these usual indicators unreliable.