| Total iron-binding capacity | |
|---|---|
 Thetransferrin protein binds freeiron and transports it in the blood. | |
| Synonyms | Transferrin iron-binding capacity |
| MedlinePlus | 003489 |
| LOINC | 2500-7,14800-7,35215-3 |
Total iron-binding capacity (TIBC) or sometimestransferrin iron-binding capacity is a medical laboratory test that measures the blood's capacity to bindiron withtransferrin.[1]Transferrin can bind two atoms offerric iron (Fe3+) with high affinity. It means thattransferrin has the capacity to transport approximately from 1.40 to 1.49 mg ofiron per gram oftransferrin present in the blood.[2]
It is performed bydrawing blood and measuring the maximum amount of iron that it can carry, which indirectly measurestransferrin[3] since transferrin is the most dynamic carrier. If TIBC values are known, the transferrin concentration can be estimated with the following formulas:[2]
To measure TIBC in the blood is less expensive than a direct measurement oftransferrin.[4][5]
The TIBC should not be confused with theunsaturated iron-binding capacity orUIBC (LOINC2501-5,22753-8 &35216-1). The UIBC is calculated by subtracting the serum iron from the TIBC.[6]
Taken together withserum iron andpercent transferrin saturation clinicians usually perform this test when they are concerned aboutanemia,iron deficiency oriron deficiency anemia. However, because theliver produces transferrin, alterations in function (such ascirrhosis,hepatitis, orliver failure) must be considered when performing this test. It can also be an indirect test of liver function, but is rarely used for this purpose.[7]
The percent transferrin saturation (i.e., the result of the formula of serum iron/TIBC x 100) can also be a useful indicator. Studies also revealed that a transferrin saturation (serum iron concentration ÷ total iron binding capacity) over 60 percent in men and over 50 percent in women identified the presence of an abnormality in iron metabolism (hereditary hemochromatosis, heterozygotes and homozygotes) with approximately 95 percent accuracy. This finding helps in the early diagnosis of hereditary hemochromatosis, especially while serumferritin still remains low. The retained iron in hereditary hemochromatosis is primarily deposited in parenchymal cells, with reticuloendothelial cell accumulation occurring very late in the disease. This is in contrast to transfusional iron overload in which iron deposition occurs first in the reticuloendothelial cells and then in parenchymal cells. This explains why ferritin levels remain relative low in hereditary hemochromatosis, while transferrin saturation is high.[8][9]
| Condition | Serum iron (highly variable) | Transferrin and TIBC | Percent transferrin saturation |
|---|---|---|---|
| Iron deficiency anemia | Low | High. Theliver produces more transferrin, presumably attempting to maximize use of the little iron that is available. | Low, as there is insufficient iron. |
| Anemia of chronic disease | Low, as the body holds iron intracellularly withferritin. | Low. The body produces less transferrin (but more ferritin), presumably to keep iron away frompathogens that require it for their metabolism. This is mainly regulated by increasedhepcidin production. | Normal |
| Pregnancy or use ofhormonal contraception, but without iron deficiency | Normal | High. The liver increases the production of transferrin, thus raising TIBC. | Low, as there is excess transferrin with normal serum iron levels. |
These examples demonstrate that to properly understand a value for TIBC, one also must know the serum iron, the percent transferrin saturation, and the individual clinical situation. In modern laboratory testings, serum ferritin levels are generally accepted as reliable single indicators of the presence of iron deficiency.[citation needed]
Laboratories often use different units of measurement and "normal ranges" may vary by population and the laboratory techniques used. Look at the individual laboratoryreference values to interpret a specific test (for instance, your own).[citation needed] Example reference ranges are:
μg/dL = micrograms per deciliter; μmol/L = micromoles per litre.