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Iron-Binding Capacity 

  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Eric B Staros, MD  more...
 
Updated: Jan 16, 2014
 

Reference Range

The index of transferrin present in circulating blood is the iron-binding capacity. Transferrin can be nearly one third saturated with iron. The unsaturated iron-binding capacity (UIBC) is measured using radioactive iron or spectrophotometric approaches. The sum of the UIBC and the plasma iron is the total iron-binding capacity (TIBC).[1] Direct measurement of the TIBC may also be performed.

The iron-binding capacity reference range is 255-450 μg/dL.

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Interpretation

Increases in iron-binding capacity are observed with the following:

Decreases in iron-binding capacity are associated with the following:

Increases in iron-binding capacity are observed with the following:

Decreases in iron-binding capacity are associated with the following:

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Collection and Panels

Container - Tiger-top or red tube[3]

Panels - Serum iron panel

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Background

Description

The measurement of the blood’s capacity to bind iron with transferrin is the iron-binding capacity. Total iron-binding capacity (TIBC) is an indirect method assessment of transferrin levels.

TIBC correlates with the serum transferrin level; however, the relationship is not linear over a wide range of transferrin levels. TIBC must not be confused with unsaturated binding capacity (UIBC), which represents the residual after subtraction of serum iron from TIBC. The relationship of TIBC and transferrin is disrupted in individuals with conditions that affect transferrin-binding capacity or other iron-binding proteins.

Iron overload conditions (eg, iron poisoning, hemolytic anemia, sideroblastic anemia, thalassemia, hemochromatosis, pyridoxine deficiency, aplastic anemia) are associated with an increased percentage of transferrin saturation with iron.

Iron deficiency is associated with a decreased percentage of transferring saturation, usually less than 16%.

Transferrin levels may be used in the assessment of nutritional status.

Test results are influenced by recent transfusions.[4, 5]

A decrease in TIBC of more than 20 mg/dL over 6 months was associated with a death hazard ratio of 1.57 (95% CI: 1.04-2.36; P = 0.03) compared with the stable TIBC group in a study by Bross et al.[6] Thus, a low baseline serum TIBC is associated with iron deficiency, protein emerge malnutrition, inflammation, a poor quality of life, and increased risk of mortality. A decline in TIBC is independently associated with an increased mortality risk.

Indications/Applications

Iron-binding capacity is used in the following:

  • Diagnosis of anemia
  • Screening for iron overload, acute hepatitis, and late pregnancy
  • Panel for serum iron to find out the percentage of saturation for the diagnosis of iron deficiency

Considerations

The index of transferrin present in circulating blood is the iron-binding capacity. Transferrin can be nearly one-third saturated with iron. The unsaturated iron-binding capacity (UIBC) is measured using radioactive iron or spectrophotometric approaches. The sum of the UIBC and the plasma iron is the total iron-binding capacity (TIBC).[1] Direct measurement of total iron-binding capacity may also be performed.

The TIBC is increased by estrogen and oral contraceptives. Decreases in the TIBC may be caused by asparaginase, chloramphenicol, corticotrophin, cortisone, and testosterone.

The UIBC and TIBC are usually increased in patients with iron-deficiency anemia, in whom a transferrin saturation of 15% or less is noted. Exceptions to this rule detract considerably from the diagnostic value of measuring transferrin saturation in patients with suspected iron deficiency.[1, 7] A low serum iron concentration is typically present along with a normal transferrin saturation in individuals with anemia of chronic inflammation.[1]

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Contributor Information and Disclosures
Author

Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP Associate Professor of Medicine, St Louis University School of Medicine

Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP is a member of the following medical societies: American College of Physicians, American Medical Informatics Association, Royal College of Physicians and Surgeons of Glasgow, Royal College of Surgeons of Edinburgh, Healthcare Information and Management Systems Society

Disclosure: Nothing to disclose.

Chief Editor

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

References
  1. Beutler E. Disorders of Iron Metabolism. Prchal JT KK, Lichtman MA, Kipps TJ, Seligsohn U, ed. Williams Hematology. 8th ed. New York: McGraw-Hill; 2010.

  2. Williamson MA, Snyder LM, Wallach JB. Wallach's interpretation of diagnostic tests. 9th ed. Wolters Kluwer/Lippincott Williams & Wilkins Health: Philadelphia; 2011.

  3. Gomella LG HS. Laboratory Diagnosis: Chemistry, Immunology, Serology. Gomella LG HS, ed. Clinician's Pocket Reference. 11 ed. New York: McGraw-Hill: The Scut Monkey; 2007.

  4. Sargent PJ, Farnaud S, Evans RW. Structure/function overview of proteins involved in iron storage and transport. Curr Med Chem. 2005. 12(23):2683-93. [Medline].

  5. Coyne D. Iron indices: what do they really mean?. Kidney Int Suppl. 2006 May. S4-8. [Medline].

  6. Bross R, Zitterkoph J, Pithia J, et al. Association of serum total iron-binding capacity and its changes over time with nutritional and clinical outcomes in hemodialysis patients. Am J Nephrol. 2009. 29(6):571-81. [Medline]. [Full Text].

  7. Driggers DA, Reeves JD, Lo EY, Dallman PR. Iron deficiency in one-year-old infants: comparison of results of a therapeutic trial in infants with anemia or low-normal hemoglobin values. J Pediatr. 1981 May. 98(5):753-8. [Medline].

  8. Hawkins RC. Total iron binding capacity or transferrin concentration alone outperforms iron and saturation indices in predicting iron deficiency. Clin Chim Acta. 2007 May 1. 380(1-2):203-7. [Medline].

 
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