Serum iron
Encyclopedia
Serum
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

 iron
is a medical
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 laboratory test that measures the amount of circulating iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 that is bound to transferrin
Transferrin
Transferrins are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids. In humans, it is encoded by the TF gene.Transferrin is a glycoprotein that binds iron very tightly but reversibly...

. Clinicians order this laboratory test when they are concerned about iron deficiency
Iron deficiency (medicine)
Iron deficiency is one of the most common of the nutritional deficiencies. Iron is present in all cells in the human body, and has several vital functions...

, which can cause anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

 and other problems.

65% of the iron in the body is bound up in hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 molecules in red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

s. About 4% is bound up in myoglobin
Myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

 molecules. Around 30% of the iron in the body is stored as ferritin
Ferritin
Ferritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. The protein is produced by almost all living organisms, including bacteria, algae and higher plants, and animals...

 or hemosiderin
Hemosiderin
thumb|Hemosiderin image of a kidney viewed under a microscope. The brown areas represent hemosiderinHemosiderin or haemosiderin is an iron-storage complex. It is always found within cells and appears to be a complex of ferritin, denatured ferritin and other material...

 in the spleen
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

, the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

 and the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

. Small amounts of iron can be found in other molecules in cells throughout the body. None of this iron is directly accessible by testing the serum.

However, some iron is circulating in the serum. Transferrin is a molecule produced by the liver that binds one or two iron(III) ions; transferrin is essential if stored iron is to be moved and used.

Most of the time, about 30% of the available sites on the transferrin molecule are filled. The test for serum iron uses blood drawn from vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

s to measure the iron molecules that are bound to transferrin, and circulating in the blood.

The extent to which sites on transferrin molecules are filled by iron ions can be another helpful clinical indicator, known as percent transferrin saturation. Another lab test saturates the sample to measure the total amount of transferrin; this test is called total iron-binding capacity
Total iron-binding capacity
Total iron-binding capacity is a medical laboratory test that measures the blood's capacity to bind iron with transferrin. It is performed by drawing blood and measuring the maximum amount of iron that it can carry, which indirectly measures transferrin since transferrin is the most dynamic carrier...

 (TIBC). These three tests are generally done at the same time, and taken together are an important part of the diagnostic process for conditions such as anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, iron deficiency anemia
Iron deficiency anemia
Iron-deficiency anemia is a common anemia that occurs when iron loss occurs, and/or the dietary intake or absorption of iron is insufficient...

, anemia of chronic disease
Anemia of chronic disease
Anemia of chronic disease, also referred to as anemia of inflammatory response is a form of anemia seen in chronic illness, e.g. from chronic infection, chronic immune activation, or malignancy...

 and Haemochromatosis
Haemochromatosis
Haemochromatosis type 1 is a hereditary disease characterized by excessive intestinal absorption of dietary iron resulting in a pathological increase in total body iron stores. Humans, like most animals, have no means to excrete excess iron...

.

Normal values

Normal reference ranges are:
  • Serum Iron (SI):
    • Men: 65 to 176 μg/dL
    • Women: 50 to 170 μg/dL
    • Newborns: 100 to 250 μg/dL
    • Children: 50 to 120 μg/dL
  • TIBC
    Total iron-binding capacity
    Total iron-binding capacity is a medical laboratory test that measures the blood's capacity to bind iron with transferrin. It is performed by drawing blood and measuring the maximum amount of iron that it can carry, which indirectly measures transferrin since transferrin is the most dynamic carrier...

    : 240–450 μg/dL
  • Transferrin saturation
    Transferrin saturation
    Transferrin saturation, abbreviated as TSAT and measured as a percentage, is a medical laboratory value. It is the ratio of serum iron and total iron-binding capacity, multiplied by 100. Of the transferrin that is available to bind iron, this value tells a clinician how much serum iron is actually...

    : 20–50%


μg/dL = microgram
Microgram
In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...

s per deciliter.

Laboratories often use different units and "normal" may vary by population and the lab techniques used; look at the individual laboratory reference values to interpret a specific test (for instance, your own).

Further reading

  • Medline Plus Medical Encyclopedia: Serum Iron.
  • Schrier SL. Regulation of iron balance. Up-to-Date. Accessed December 5, 2005. (Requires subscription.)
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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