Transferrin

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Transferrin is a beta-globulin that carries iron through blood. It is synthesized in the liver.

Role and receptors

It binds to two receptors, transferrin receptor 1 (TfR1) on all cells that use iron, and TfR2 on enterocytes in the duodenum.[1]

Use in diagnosis

The transferrin level, usually measured as indirectly as the total iron binding capacity (TIBC) is one of the tests used in the differential diagnosis of anemia, the other major biochemical measurements being serum iron (SI), and serum ferritin. While serum iron varies greatly, among individuals,also in response to iron intake, the other two parameters mentioned change in an acute phase reaction (ferritin rises and transferrin fslls) and thus cannot reliably detect iron deficiency in the presence of inflammation. They also do not measure if the iron is actually available for hematopoiesis. [2]

Transferrin saturation

One way to correct for the effect of inflammation is to calculate the percentage of transferrin saturation (TfS or TSAT):[3]

TSAT = SI/TIBC
  • TSAT < 20: iron deficiency
  • TSAT > 30 & TSAT < 50: normal
  • TSAT > 50: iron overload

Alternative tests

Newer tests that circumvent this problem include soluble transferrin receptor (sTfr), the hemoglobin content of reticulocytes or the percentage of hypochromic cells.

Likelihood ratios for common tests[4]
Test Cutoff value Likelihood ratio
Transferrin saturation ≥ 50% 0.15
Transferrin saturation ≤ 5% 10.46
A likelihood ratio > 10 helps establish a diagnosis while a ratio < 0.1 helps exclude a diagnosis.[5]

References

  1. Munoz M, Villar I, Garcia-Erce JA (2009), "An update on iron physiology", World J Gastroenterol 15 (37): 4617–4626., DOI:10.3748/wjg.15.4617.
  2. Thomas C, Thomas L (2002). "Biochemical Markers and Hematologic Indices in the Diagnosis of Functional Iron Deficiency". Clin Chem 48 (7): 1066-76. PMID 12089176.
  3. Fauci A et al., ed. (1998), Chapter 106: Iron Deficiency and Other Hypoproliferative Anemias, Harrison's Principles of Internal Medicine (14th ed.), McGraw-Hill, p. 641
  4. Guyatt GH, Oxman AD, Ali M, Willan A, McIlroy W, Patterson C (1992). "Laboratory diagnosis of iron-deficiency anemia: an overview". J Gen Intern Med 7 (2): 145–53. PMID 1487761[e]
  5. McGee S (August 2002). "Simplifying likelihood ratios". J Gen Intern Med 17 (8): 646–9. PMID 12213147[e]