Screening for chronic iron overload diseases, particularly hereditary hemochromatosis
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Transferrin is a glycoprotein with a molecular weight of 79570 daltons. It consists of a polypeptide strand with 2 N-glycosidically linked oligosaccharide chains and exists in numerous isoforms. The rate of synthesis in the liver can be altered in accordance with the bodyâ€™s iron requirements and iron reserves. Transferrin is the iron transport protein in serum. In cases of iron deficiency, the degree of transferrin saturation appears to be an extremely sensitive indicator of functional iron depletion. The ferritin levels are depressed when there is a deficiency of storage iron. In sideropenia, an iron deficiency can be excluded if the serum transferrin concentration is low, as in inflammation or less commonly, in cases of ascorbic acid deficiency. In screening for hereditary hemochromatosis, transferrin saturation provides a better indication of the homozygous genotype than does ferritin. The treatment of anemia with erythropoietin in patients with renal failure is only effective when sufficient depot iron is present. The best monitoring procedure is to determine transferrin saturation during therapy. Transferrin saturation in conjunction with ferritin gives a conclusive prediction of the exclusion of iron overloading in patients with chronic liver disease.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Serum iron, total iron binding capacity (TIBC), and percent saturation are useful only in screening for chronic iron overload diseases, particularly hereditary hemochromatosis. Although serum iron, TIBC, and percent saturation are widely used for the diagnosis of iron deficiency, serum ferritin is a much more sensitive and reliable means of demonstrating iron deficiency.
In hereditary hemochromatosis, serum iron is usually >150 mcg/dL and percent saturation exceeds 60%.
In advanced iron overload states, the percent saturation often exceeds 90%.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Measurement of serum iron, iron binding capacity, and percent saturation should not be used as the primary test for iron deficiency. It may be helpful in conjunction with ferritin and soluble transferrin receptor, especially in patients with inflammation.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Silverman LM, Christenson RH, Grant GH: Amino acids and proteins. In Textbook of Clinical Chemistry. Edited by NW Tietz. Philadelphia, WB Saunders Company, 1986, pp 519-618
2. Ramsay WNM: The determination of the total iron binding capacity of serum. Clin Chim Acta 1957;1:221-226
3. Tsung SH, Rosenthal WA, Milewski KA: Immunological measurement of transferrin compared with chemical measurement of total iron binding capacity. Clin Chem 1975;21:1063-1066
4. Buffone GJ, Lewis SA, Losefsohn M, Hicks JM: Chemical and immunochemical measurements of total iron binding capacity compared. Clin Chem 1978;24:1788-1791
5. Markowitz H, Fairbanks VF: Transferrin assay and total iron binding capacity. Mayo Clin Proc 1983;58:827-828
6. Szoke D, Panteghini M: Diagnostic value of transferrin. Clin Chim Acta 2012 Aug 16;413(15-16):1184-1189