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  Back Blood-tests Explained


Serum Iron


At a Glance

Why Get Tested?

To determine your blood iron level

When to Get Tested?

When your doctor suspects that you may have too little or too much iron in your body

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

You may be instructed to fast for 12 hours before sample collection; in this case, only water is permitted.

The Test Sample

What is being tested?

Iron is an essential trace element and nutrient that is necessary to maintain life. The serum iron test measures the amount of iron in the liquid portion of blood.

Iron is absorbed from food and transported throughout the body by transferrin, a protein produced by the liver. Iron is necessary for the production of healthy red blood cells (RBCs). It is an important part of hemoglobin, the protein in RBCs that enables them to carry oxygen throughout the body.Iron is also used in the production of some proteins, including myoglobin and some enzymes.

Normally, about 70% of the iron absorbed is incorporated into the production of hemoglobin inside RBCs. The remainder is stored in the tissues as ferritin or hemosiderin.If not enough iron is taken in from the diet, blood levels will drop; thus, over time, the iron stored in the tissues will be used, eventually depleting the stored iron. Insufficient levels of circulating iron and iron storage will eventually lead to iron deficiency anemia.On the other hand, absorption of too much iron can lead to progressive accumulation and damage to organs such as the liver, heart, and pancreas.

The serum iron test measures the amount of iron that is in transit in the body – the iron that is bound to transferrin.The amount of iron present in the blood will vary throughout the day and from day to day. For this reason, serum iron is almost always measured with other iron tests, such as serum ferritin and the total iron-binding capacity (TIBC), from which the transferrin saturation can be calculated. Transferrin saturation reflects the amount of iron being transported in the blood and its capacity to carry more. The use of several iron tests provides a more reliable measure of iron deficiency and iron overload than measuring serum iron by itself.

How is the sample collected for testing?

A blood sample is drawn by needle from a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

Morning samples are preferred. Fasting for 12 hours before sample collection may be required.In this case, only water is permitted.

The Test

How is it used?

Serum iron, total iron-binding capacity (TIBC), and/or transferrin tests are usually ordered together and, subsequantly, the transferrin saturation can be determined and used to assess how much iron is being carried in the blood.A ferritin test may also be used to evaluate a person's current iron stores.

These tests are used together to detect and help diagnose iron deficiency or iron overload.In people with anemia, these tests can help determine whether the condition is due to iron deficiency or another cause, such as chronic blood loss or some other illness.Iron tests are also ordered if a doctor suspects that a person has iron poisoning and to screen for hereditary hemochromatosis, an inherited condition associated with excessive iron storage.

When is it ordered?

Serum iron tests are typically ordered as follow-up tests when abnormal results are found on routine tests such as a CBC, with decreased hemoglobin and hematocrit levels.They may also be ordered when iron deficiency or iron overload is suspected.

Early iron deficiency often goes unnoticed. If a person is otherwise healthy, symptoms seldom emerge before the hemoglobin in the blood drops below a certain level (about 10 g per deciliter). As iron storage depletion progresses and anemia begins to develop, some of the following signs and symptoms may appear:

  • Chronic fatigue/tiredness
  • Dizziness
  • Weakness
  • Headaches
  • Pallor

If the iron-deficiency anemia is severe, shortness of breath, dizziness, chest pain, headaches, and leg pains may occur. Children may develop learning (cognitive) disabilities if the deficiency persists. Besides the general symptoms of anemia, there are certain symptoms that are characteristic of iron deficiency. These include pica (cravings for specific substances, such as licorice, chalk, dirt, or clay), a burning sensation in the tongue or a smooth tongue, sores at the corners of the mouth, and spoon-shaped fingernails and toenails.

A serum iron and other iron tests may be ordered when iron overload (hemochromatosis) is suspected.Symptoms of high iron levels will vary from person to person and tend to worsen over time.They are associated with iron accumulation and can be similar to those seen with other conditions.Symptoms may include:

  • Joint pain
  • Fatigue, weakness
  • Lack of energy
  • Abdominal pain
  • Loss of sex drive
  • Heart problems

When a child is suspected to have ingested iron tablets, a serum iron test is ordered to detect and help assess the severity of the poisoning.Iron tests may also be ordered periodically when iron deficiency or overload is being treated to evaluate the effectiveness of treatment.

What does the test result mean?

Serum iron levels are often evaluated in conjunction with other iron tests. A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.

 

Disease Iron TIBC/Transferrin UIBC

%Transferrin

Saturation

 Ferritin
Iron Deficiency Low High High Low Low
Hemochromatosis High Low Low High High
Chronic Illness Low Low Low/Normal Low Normal/High
Hemolytic Anemia High Normal/Low Low/Normal High High
Sideroblastic Anemia Normal/High Normal/Low Low/Normal High High
Iron Poisoning High Normal Low High Normal

A low iron with a high transferrin or TIBC is usually due to iron deficiency. In chronic diseases, both iron and transferrin or TIBC are typically low. Iron deficiency is usually due to long-term or heavy bleeding.However, it can also be due to increased iron requirements (in pregnancy), rapid growth (in children), poor diet, and problems with absorption (stomach or intestinal disease). Infants between the ages of 6 months and 24 months who are not being breast-fed are particularly susceptible to iron deficiency if supplemental dietary iron is not provided.

High levels of serum iron can occur as the result of multiple blood transfusions, iron injections into muscle, lead poisoning, liver disease, or kidney disease. It can also be due to the genetic disease, hemochromatosis.

Is there anything else I should know?

Recent consumption of iron-rich foods or iron pills can affect test results, as can recent blood transfusions.Alcohol and drugs, such as oral contraceptives and methotrexate, can increase iron test levels, while testosterone, large doses of aspirin, metformin, and ACTH (adrenocorticotropic hormone) can decrease them.

Stress and sleep deprivation can temporarily decrease serum iron levels.



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